NO328556B1 - Electric power distribution and communication system for an underwater cable - Google Patents

Description

The present invention requires the benefit of US Provisional Application No. 60/004,203, filed September 22, 1995, which is incorporated herein by reference, US Provisional Application No. 60/004,209, filed September 22, 1995, which is incorporated herein by reference by reference, US Provisional Application No. 60/005,500, filed September 22, 1995, which is incorporated herein by reference, US Provisional Application No. 60/004,493, filed September 22, 1995, and which is incorporated herein by reference, and US Provisional Application No. 60/004,494, filed September 22, 1995, which is incorporated herein by reference.

Field of the invention

The present invention relates to underwater cable arrangements and more specifically equipment for communication with and power supply to electrical devices, such as sensors and cable regulator devices, which are located at separate locations along an instrumented underwater cable, such as a towed seismic hydrophone cable used in seismic surveys for sea or other purposes.

The background of the invention

Trailed seismic hydrophone cable assemblies typically comprise multiple electrically separated devices located at selected locations along the cable.

In the event that the electrical devices are applied around the outside of the towed seismic hydrophone cable, they are usually called wet units. In many applications, the wet units are inductively coupled to data communication lines within the seismic hydrophone cable.

One or more of the seismic hydrophone cable assemblies may be towed by an exploration vessel. The wet units communicate with electronic equipment at the dry end, e.g. on the search vessel, over one or more communication channels. Communication channels between the wet units and the electronic equipment at the dry end usually comprise a communication line which is single-ended or consists of twisted pairs of wires, and is connected to the wet units. Electromagnetic coupling can be used to enable communication with the wet units without breaking the outer covering of the towed seismic hydrophone cable.

Typically, each of the wet units receives any power from a battery located inside the wet unit. The use of batteries as the primary power source in the various separate electrical devices may be required in practical applications due to low coupling coefficients between the underwater cable and the wet units. However, using batteries as a primary power source is often undesirable, as the batteries may require replacement every few weeks or months. Replacement of batteries usually entails removal of the wet units when the seismic cable has been taken up and is present as cable coils on the exploration vessel. The wet units are then operated separately by opening the relevant unit and replacing and/or recharging the existing batteries. This battery maintenance process can be very inefficient and lead to unwanted downtime. When lithium batteries are used, the costs of scrapping and replacing the batteries for a single vessel can exceed several hundred thousand dollars per vessel. year. The usual wet unit constructions therefore entail several disadvantages.

A major problem associated with the omission of batteries from the wet unit devices is the low coupling coefficient between the wet units and the underwater cable. Although numerous attempts have been made to improve this coupling coefficient, the results of these attempts have been found to be unsatisfactory.

US Patent No. 4,912,684 in the name of John T. Fowler describes a communication system that transmits both power and data signals along a one-conductor or two-conductor transmission line extending the length of the submarine cable. Power signals can be used to charge batteries in the wet units, such as in cable level units applied along the cable. The power and data signals are then inductively coupled between the transmission line and the wet units using coils that are connected to the transmission line at specific locations along the hydrophone cable as well as assigned coils inside each level unit. However, due to several technical difficulties, a seismic hydrophone cable assembly that transmits operating power from the underwater cable directly to the wet units or to the wet units and devices in the hydrophone cable has not yet proven to be commercially practical.

The patent document EP 0 330 784 B1 mentions a communication system for a seismic streamer where all power and data signals are inductively coupled to cable level devices (12) or instrumentation pods placed along the streamer cable.

Common transmission lines are e.g. typically configured as continuous unbroken transmission lines running the length of the hydrophone cable, which has typically had a length of approx. 6 km or less. Transmission losses in such transmission lines in underwater hydrophone cables with a length of more than 6 km drastically increase the present problems when powering the separate electrical devices directly from the underwater hydrophone cable. Furthermore, the data and/or the power transmitted to the electrical devices at the aft end of the underwater cable will often be seriously weakened. This problem can be particularly acute when data lines are also used for power transmission. It has been found that transmission line losses and noise levels in such a system often make the equipment commercially impractical. Communication with and power supply to electrical equipment at the outer end of the cable can then be difficult, especially with ever-increasing cable lengths. Much research has been carried out to solve this problem, but so far with very little success.

An attempt has been to resort to wire with a large cross-section and increase the power level when transferring to the cable. However, this cannot usually be accepted as additional weight is applied to the underwater cable and the higher power levels can affect the operation of the seismic equipment, such as underwater hydrophones.

Another disadvantage of conventional power distribution and/or data communication systems is that the inductive circuits used for coupling between the underwater cable and the wet units must be precisely matched within narrow margins to ensure sufficient coupling to transfer power and data to and from the electrical devices . If an electrical device fails, falls off or is otherwise damaged or removed from the underwater cable, the associated coil on the transmission line will have an open secondary winding, which will bias the tuned circuit. Often the transmission line can be tuned to a point where reliable data and power transmission can hardly take place.

In typical underwater sonar cables, it is difficult to transmit power along the cable at high frequency due to the length of the cable, the amount of power that is required to be distributed, as well as the noise produced by such a transmission. Consequently, power is usually transmitted at a low frequency along the entire length of the cable. However, low-frequency signals are extremely inefficient when it comes to coupling via a transformer with a low coupling coefficient. Designs for connecting power from the main power line can thus be commercially impractical in many applications.

Another shortcoming of conventional power distribution and/or data communication systems for hydrophone cables can be reliability problems due to leakage of seawater into one or more sections of the hydrophone cable. When seawater leaks into a section of the submarine cable, a low-impedance current path or short circuit can form across the transmission line. In a transmission line with continuous conductor wire over the entire length of the underwater cable, such a short circuit can put the entire transmission line out of service. When the transmission line is taken out of service, sensor data cannot be collected, the electrical devices cannot be supplied with power from the underwater cable, and the submersion regulation from the exploration vessel can be ineffective.

There is therefore a need for a power distribution and/or data communication system for underwater cables that can overcome the stated and other problems, as well as enable very efficient and reliable transmission of power and data between the underwater cable and the electrical devices even under demanding operating conditions.

Summary description of the invention

A main purpose of the present invention is to produce a power transmission and/or data communication system which can provide reliable power distribution and

data transmission to several electrical devices arranged along an underwater cable. Such a power distribution and/or data communication system can then also constitute improved construction and/or operation that increases the reliability of a seismic hydrophone cable assembly, even in the event that the cable is damaged and/or electrical devices are removed.

Further objects and various aspects of the present invention include the creation of an underwater cable construction that enables the transmission of operating power to the electrical devices without breaking the outer covering of the underwater cable, eliminating batteries as the primary source of operating power for the electrical devices connected to the underwater cable, eliminating and/or or reduction of the need to replace batteries, create better economy by allowing a submarine cable assembly to be in exploration operation for several hours without interruption, extend the operational length of submarine cables by 5, 10, 15, 20 km without changing the basic construction and /or operation of the submarine cable's power distribution and/or data communication, increasing the bandwidth of data transmitted to and received from the electrical devices, increasing the efficiency of the power transmission from a main power source to the electrical devices arranged along the underwater cable, reducing the noise that developed during the power transmission and which can disturb the seismic equipment, reduction of capacitive coupling and mutual inductance between the electrical devices and other parts of the underwater cable, improvement of the coupling coefficient for a transformer arranged around the outer covering of the underwater cable, creation of a fault-tolerant power transmission and data communication system in an underwater cable assembly, reduction of the number of data and power transmission lines that are connected to each of the electrical devices and arranged in the underwater cable, reduction of the waiting time associated with communications with the electrical devices through the underwater cable, creating the possibility for the electrical devices to react directly to detected fault conditions without interference from electronics in the dry end, as well as create opportunities for operation in degraded mode to allow the most critical work operations for the electrical equipment to be maintained even during fe fire conditions.

According to the present invention, an underwater power distribution system has thus been produced which comprises an underwater cable for power supply of several electrical devices which are arranged along the cable. A main power line runs through the underwater cable. Two or more distribution lines as well as two or more power distributors are also arranged in the underwater cable. Each power distributor is electrically connected between the main power line and one of the power distribution lines to transfer power from the main power line to the associated power distribution line. One or more power couplers are arranged at selected locations along the underwater cable. Each power distribution line is connected to one or more power couplers next to one of the electrical devices for connecting power to the adjacent device.

In underwater systems that utilize this aspect of the invention, power can be transmitted along the main power line and then distributed to the electrical devices using power distribution lines. Each power distribution line distributes power directly to small subsets of electrical devices. This arrangement is particularly advantageous. It allows both power transmission along the main power line and power distribution along the distribution lines to be independently optimized regardless of the length of the subsea cable assembly, resulting in a highly reliable and efficient subsea power distribution system. Systems that make use of this aspect of the invention are so reliable and so efficient that batteries can either be eliminated entirely from the electrical devices or used in rare cases as fail-safes. Such an embodiment of the invention thus almost completely eliminates economic losses when taking up an underwater cable and replacing or recharging the batteries in the electrical devices, and thus greatly extends the operating life of an underwater cable assembly.

This arrangement of a main power line and several power distribution lines additionally allows segmentation of the submarine cable assembly. Each power distribution line and the subgroup of electrical devices connected to this power distribution line can then form a separate section of the underwater cable assembly. This arrangement further increases the reliability of a submarine cable assembly, as it provides a highly fault-tolerant system. Each section can then have fault protection features that isolate a fault, such as seawater intrusion or loss of an electrical device, in that section, but maintain power transmission and data communication to the remaining sections of the submarine cable assembly. Segmentation of the submarine cable assembly makes it easy to extend the cable assembly simply by adding additional sections, that is, by extending the main power line and adding additional power distribution lines.

The present invention also applies to an underwater power distribution system for power supply of electrical devices. This underwater power distribution system comprises an underwater cable comprising two or more electronic hydrophone cable modules as well as two or more cable sections. At least one of the electrical devices is arranged along each cable section, and the hydrophone electronics modules are arranged alternating with the cable sections and at a distance from the electrical devices. A main power line runs through the underwater cable. Two or more power distribution lines are arranged in the underwater cable, with at least one power distribution line extending through each cable section. Each hydrophone electronics module includes a circuit for coupling electrical power from the main power line to a nearby power distribution line. Two or more power couplers are arranged at selected locations along the underwater cable. Each power distribution line is connected to one or more power couplers, and each power coupler is placed close to at least one of the electrical devices in order to connect power to this nearby device.

Systems utilizing this aspect of the present invention can be similar and have many of the same advantages as the previously described underwater power distribution system. In systems that utilize this aspect of the present invention, however, the underwater cable comprises alternately arranged hydrophone electronics modules and cable sections, and at least one power distribution line is branched off from the main power line by a hydrophone electronics module. This arrangement makes it possible for a large part of the electrical circuits, including power supplies, data circuits, and circuit boards to be able to be combined with existing circuit equipment in the hydrophone electronics modules, and will therefore significantly reduce the extra weight and complexity added to the underwater cable assembly for to be able to achieve power transmission to the power distribution lines.

The present invention specifies a method for distributing power under water to one or more electrical devices which are arranged along an underwater cable. This method includes transmission of power at the first frequency on a main power line in the underwater cable, transmission of the power on the main power line to another frequency that is higher than the first frequency, as well as distribution of the power at the second frequency over two or more power distribution lines to the electrical devices. The first frequency can be either zero frequency, corresponding to direct current, or an alternating current frequency with a value greater than zero.

The invention also applies to an underwater power distribution system for the power supply of two or more electrical devices. This underwater power distribution system comprises an underwater cable and the devices arranged along the underwater cable. A main power line extends through the underwater cable and is arranged to transmit a main power signal at the first frequency. Several converter circuits are arranged at separate locations along the underwater cable and are connected between the main power line and each electrical device. Each conversion circuit is arranged to convert the main power signal into a power distribution signal at a different frequency which is higher than the first frequency.

In methods and equipment that utilize these aspects of the present invention, power is transmitted along the main power line at a certain frequency and distributed to the electrical devices along the underwater cable at a higher frequency. This arrangement greatly increases the power transfer efficiency along the main line and to the electrical devices. Transmission of power at a relatively low frequency along the main power line makes it possible to transmit power most efficiently to the aft end of the underwater cable. Transforming the main power signal at the lower frequency into a power distribution signal at a higher frequency makes it possible to distribute the power extremely efficiently from the main power line to the electrical devices. This is particularly advantageous in cases where the electrical devices are mounted on the outside of the underwater cable and power is connected inductively or capacitively through the underwater cable's cover without any physical conductor connection penetrating through the cover. The high-frequency signal couples power inductively through the overdraft much better than a low-frequency signal.

In some embodiments that utilize these aspects of the invention, it may be desirable to first transfer the main power signal to a direct current signal and then to transform the direct current signal into a power distribution signal with a higher frequency. The conversion first to a DC signal can further improve the efficiency of the power conversion process.

According to the invention, an underwater power distribution system for the transmission of power is produced. This underwater power distribution system comprises an underwater cable and two or more electrical devices which are arranged at selected locations along the underwater cable. The underwater cable has an outer covering which is filled with a lossy dielectric material with a loss factor of about 1.01 or greater. A main power line runs through the underwater cable. Several pairs of twisted insulated transmission lines extend through the underwater cable and are connected between the main power line and the electrical installations. Each pair of twisted transmission lines has an outer covering and a loss factor less than approx. 0.01 when surrounded by the lossy dielectric material.

Equipment utilizing this aspect of the invention is capable of very efficiently transmitting power along the underwater cable to electrical devices, even in the event that the underwater cable is filled with a lossy dielectric material, such as a non-aqueous fluid that maintains the underwater cable in a neutral buoyancy- state. By providing the transmission lines with an outer covering that has a loss factor less than approx. 0.01 in the lossy material, power can still be transferred very efficiently along the underwater cable and through the power distribution lines to the electrical devices.

The invention also applies to an underwater system for distributing power to communicate with two or more electrical devices. This underwater system

comprises an underwater cable where the electrical devices are arranged at selected locations along the cable. Each device includes one or more loads. A first line extends through the underwater cable and is connected to the electrical devices. Fault detection circuits are connected to the first line to detect when a fault is present. Disconnect circuits are connected to the fault detection circuits to disconnect one or more of the loads in a hierarchical order in response to a fault.

The invention also applies to a method for distributing power along an underwater transmission system. This underwater transmission system comprises an underwater cable with two or more electrical devices distributed along the underwater cable, each such device comprising one or more loads. The procedure involves electrical signals being transmitted along the underwater cable, faults in the underwater transmission system are detected, loads are removed along the underwater cable in a hierarchical order in response to the fault, while the remaining loads are supplied with power.

The invention further relates to a method for distributing both power and data along an underwater cable. Two or more electrical devices at a distance from each other are connected to the underwater cable, and each such device includes one or more electrical loads. The procedure involves power and data being transmitted along a line in the underwater cable, a fault is detected and one or more of the electrical loads are removed by choice from the underwater cable according to a predetermined hierarchy in response to the fault.

Equipment and methods that utilize these aspects of the present invention respond to a fault in a power line or a data distribution line by selectively removing, that is to say disconnecting, different loads and supplying functions in a regulated, hierarchical manner. The least important functions or electrical devices are disconnected first and the most important functions and electrical devices are disconnected last. Alternatively, all electrical devices or functions can be switched off as a reaction to the fault, after which the most important electrical devices are switched on in a regulated, hierarchical manner as and when sufficient power is available.

Such management increases the chances of survival for the more critical functions or devices in its damaged section of the cable, as well as the chances of survival for the other functions or devices located in undamaged sections of the cable. Exclusion of electrical loads that are assigned to different functions or devices, as well as hierarchical load disconnection in particular, is even more important in cases where both power and data are transmitted over a single distribution line. Load disconnection allows the transfer of power and communications to or from downstream electrical devices and remain operational even when an intermediate cable section has been damaged.

According to the invention, an underwater power distribution system has been developed for the power supply of two or more electrical devices. This underwater power distribution system comprises an underwater cable where the electrical devices are distributed at selected locations along the cable. A power line extends through the underwater cable and is connected to the electrical devices. A current limited drive circuit is connected to the power line to drive a power distribution signal on the power line at or below a predetermined current level. A fault detection circuit is also connected to the power line. The fault detection circuit includes a voltage detection circuit to detect a change in the voltage on the power line.

Equipment that utilizes this aspect of the invention has the possibility of quickly detecting a fault, each of the electrical devices or each section of the underwater cable without interference from the search vessel. When the current on each power line is limited, e.g. a short circuit or other current leakage fault, such as in the case of seawater inflow, cause a voltage drop to occur on the power distribution lines. A fault (e.g. seawater intrusion) can then be detected simply by monitoring a voltage received from the power line, e.g. by detecting a reduction in the voltage on the power line. Furthermore, the current-limited drive not only provides autonomous fault detection, but also prevents a section of the underwater cable from exceeding a predetermined power budget due to the fault. Excessive power extraction from one or more cable sections can adversely affect the entire underwater cable's operational function.

Furthermore, in accordance with the invention, an underwater power/data transmission system has been produced which comprises a sub-cable and a mechanism assigned to the cable for transmitting power and/or data along, into or out of the cable.

The invention further relates to a device assigned to an underwater cable and which comprises a mechanism for sending, receiving or producing power and/or data.

The invention further relates to an underwater data communication system for communicating with several electrical devices, and comprises a primary data communication circuit, a back-up communication circuit, as well as circuits connected to the primary data communication circuit and the back-up data communication circuit for switching between the primary data communication circuit and the back-up data communication circuit as a reaction on a loss of power to the electrical devices.

According to the invention, an underwater communication system has been created for communicating with two or more electrical devices. This underwater communication system comprises an underwater cable with electrical devices arranged at selected locations along the underwater cable. An incoming data distribution line and an outgoing data distribution line extend through the underwater cable and are connected to one or more of the electrical devices. At least one amplifier circuit is arranged in the underwater cable. The amplifier circuit comprises synchronizing circuits connected to the input and output data distribution lines to derive clock data from the output data and transmit the input data in accordance with the derived clock data, so that a time connection is established between input and output data.

The invention also applies to a method for communicating data underwater. The method then involves transmitting outgoing data and incoming data through an amplifier circuit in an underwater cable, decoding the outgoing data in the amplifier circuit to derive clock data, and transmitting incoming data from the amplifier circuit in synchronism with said clock data.

The invention further relates to a further method for communicating data underwater. This method involves outgoing data being received along an underwater cable, the outgoing data being decoded to extract a clock signal, and incoming data being transmitted along the underwater cable in synchronism with this clock data.

In equipment and methods utilizing these aspects of the invention, incoming data along the underwater cable is synchronized in accordance with a clock rate derived from outgoing data. Synchronization of incoming data with outgoing data by means of amplifiers, electrical devices and dry-end electronic equipment greatly reduces dead time, namely the time delay that occurs when an incoming electrical signal is sent from an electrical device, resulting in more efficient utilization of the available bandwidth. Since the electrical devices are already synchronized with each of the amplifiers and the electronics in the dry end, there is no further need to send out a long block warning to achieve synchronization with each amplifier and the dry end electronics. In accordance with these aspects of the invention, data can then be sent inbound from the electrical devices to the search vessel very quickly and efficiently.

In accordance with the invention, an underwater system for transmitting power has been developed. This system for transmitting power under water comprises an underwater cable and two or more wet units which are arranged at selected locations along the underwater cable. Each wet unit has a first inductor to receive power. The underwater cable comprises two or more other inductors, each of which is arranged close to the first inductors in the wet units. Hydrophones are also arranged at selected locations along the cable and operate in one or more first operating frequency bands. Power conversion circuits are coupled to each set of one or more other inductors to provide an output signal in a different operating frequency band to the wet units. The first working frequency band and the second working frequency band do not overlap.

The invention also applies to a method for transferring power under water. This method involves arranging hydrophones in an underwater cable that work in one or more first frequency bands, as power is transferred inductively from an underwater cable to two or more wet units in another frequency band that does not overlap the first frequency bands.

Frequency band separation was found to prevent coupling of noise from the power transfer to the hydrophone circuits, even when a high power, high voltage signal was continuously active.

Furthermore, frequency band separation was found to be particularly effective at

combination with an effective filter. Effective filtering coupled with frequency limitations with regard to the power distribution signal increases the sensitivity and noise immunity of the hydrophones when the power transmission frequency of the wet units increases. In certain embodiments, an effective filter to separate the hydrophone signal frequency bands from the power transmission frequency band can be implemented by configuring the concentrated and distributed parameters of each power transmission line to form a distributed bandpass filter centered on the power transmission frequency band.

In accordance with the invention, an underwater power distribution system has been developed for the supply of electrical power to two or more electrical devices. This system for power distribution under water comprises an underwater cable with electrical devices arranged along the cable. Two or more data distribution lines extend through sections of the submarine cable. Two or more amplifier circuits are individually connected between mutually adjacent data distribution lines to form a data communication channel. Each data distribution line is connected to one or more electrical devices and is tuned to resonance at a first frequency and with a predetermined bandwidth. Each data distribution line includes at least one load control circuit to keep each data distribution line tuned to about the first frequency with the predetermined bandwidth, in response to a fault condition, e.g. a lost device, an appliance failure, or ingress of sea water.

Power distribution systems for underwater cables that utilize this aspect of the invention make it possible to continue power transmission along a certain cable section even when the relevant cable section and/or electrical equipment within the cable section has been damaged and/or removed. In the event that groups of electrical devices are buffer-coupled to amplifier units, the electrical effect in the event of the loss of a device or the intrusion of seawater into a cable section will be electrically isolated from the other cable sections. In these embodiments, the load control circuit is thus even more efficient when it comes to preventing skew tuning of a particular cable section, so that communications and power transmission can continue along the entire communication channel. Furthermore, retransmission of a message signal at a predetermined level of the amplifier at the end of the biased section with a load control circuit will overcome the biasing effects of a lost device or intrusion of seawater and enable the transmission of data to downstream devices.

In addition to an underwater cable system, the invention also relates to electrical devices for use in an underwater cable system. According to the invention, it is e.g. produced an electrical device for use together with an underwater cable and which comprises an apparatus housing, a load circuit arranged in the housing and an inductor circuit connected to the load circuit. The inductor circuit transmits a power distribution signal from the underwater cable to the load circuit, so that this load circuit receives the power distribution signal. A control circuit is connected to the inductor circuit and/or the load circuit to reduce the load in response to the power distribution signal possibly decreasing to below a predetermined ni-

o

huh.

The present invention also applies to an electrical underwater device

for an underwater cable and comprising a line to apply a voltage. The underwater electrical installation comprises an apparatus housing, at least one electrical load in the housing, as well as a control circuit in the apparatus housing. The control circuit includes circuitry for monitoring a voltage on a line in an underwater cable to reduce the electrical load in the event that the voltage should fall below a predetermined voltage level.

According to the invention, an electrical underwater device for an underwater cable has also been developed. This underwater electrical device comprises a control circuit which is designed to be connected to transmit and receive power from the underwater cable. The control circuit comprises a fault detection circuit to detect a fault as well as a load disconnection circuit to reduce the power received from the underwater cable in a hierarchical order in response to the fault.

Electrical underwater devices that utilize these aspects of the invention can autonomously detect when a fault occurs in a device or a nearby cable section, as well as automatically reduce the load on the relevant cable section regardless of receiving command signals from the cable assembly or the search vessel. In other words, the electrical devices can carry out error recovery completely autonomously without any external control from the underwater cable or the exploration vessel. In this way, reliability is increased and the underwater cable assembly can resume communications and/or power transmission over the underwater cable even in the event that communications and/or power transmission over a section of the cable has been interrupted. With hierarchical load disconnection, more important work functions for the electrical devices can be maintained in operation while less important functions are disconnected first. This enables an intelligent, hierarchically degraded mode of operation even along damaged sections of the submarine cable.

According to the present invention, an underwater electrical device for an underwater cable has been produced. This underwater electrical device comprises an apparatus housing, an input circuit and an output circuit. The apparatus housing is arranged to be connected to the underwater cable. The input circuit is arranged in the apparatus housing to receive input data from the underwater cable. The output circuit includes synchronization circuitry to derive a timing signal from data. The output circuit is connected to the input circuit and arranged to provide output data to the underwater circuit in synchronism with the time signal.

The invention also applies to an underwater coupling system comprising an underwater cable, at least one coupler and two or more induction coils. The coupler is arranged in the underwater cable and the induction coils are arranged on the outside of the underwater cable at selected locations along the perimeter around the coupler.

Underwater coupling systems that utilize this aspect of the invention have two or more coils, such as coils mounted at a distance from each other in the circumferential direction and around the coupler. This arrangement is particularly advantageous for designs where the induction coils are located in the wet units. It allows rotation of the wet units while still maintaining a high coupling coefficient at different orientations. In addition, each of the different coils may comprise a core and the coils may be electrically interconnected to further improve the coupling coefficient.

The invention further relates to an underwater coupling system which comprises an underwater cable, at least one coupler arranged in the underwater cable and several induction coils at a circumferential distance from each other inside the coupler. Equipment that includes this aspect of the invention enables the rotation of an electrical device in relation to the cable without loss of power and/or data communications with the search vessel.

The invention also applies to an underwater coupling system comprising an underwater cable and two or more inductive replicas. These inductive replicas are arranged at selected locations along the submarine cable. Each coupler comprises at least one coil with a core having a substantially triangular cross-section, as well as a winding wound around the substantially triangular core.

Underwater coupling systems utilizing this aspect of the invention exhibit excellent coupling efficiency. The triangular core provides an extremely efficient use of space inside the underwater cable, so that a relatively large core with a high coupling coefficient can be used within the mechanical limitations that exist for a coupler and/or an underwater cable.

According to the invention, an underwater connection system has also been produced which comprises an underwater cable, first and second line, as well as two or more copies. The first and second lines extend through the underwater cable and the couplers are arranged at selected locations along the cable. Each coupler comprises an integrated core with a first and second part and first and second coils which are wound around the first and second part of the integrated core, respectively. The first and second lines are respectively connected to the first and second coils.

In underwater coupling systems utilizing this aspect of the invention, each coupler comprises an integrated core. This arrangement significantly improves the coupling coefficient between the underwater cable and any electrical equipment connected to the cable at the coupler.

The invention further relates to an underwater connection system with an underwater cable, first and second lines that extend through the underwater cable, as well as two or more copies. The couplers are arranged at selected locations along the underwater cable. Each coupler comprises a first coil connected to the first line and second and third coils connected to the second line. The first and second coils are separated from each other, while the first and third coils are located close to each other to eliminate crosstalk between the first and second coils.

In underwater coupling systems that utilize this aspect of the invention, the first and third coils are arranged close to each other to prevent crosstalk between the first and second coils. This arrangement significantly reduces noise and therefore increases the reliability of communication with the electrical devices along the underwater cable.

The present invention also applies to electrical equipment for power distribution and communication and/or a coupler system with one or more of the elements described here and/or shown in fig. 1-49, in any combinations or sub-combinations. The invention is intended to encompass any number of combinations and sub-combinations of elements described and shown herein.

Further advantageous features of the present invention will appear from the associated independent patent claims, and furthermore, special embodiments will appear from the attached non-independent claims.

Brief description of the drawings

The above-described advantages, distinctive features and purpose of the invention will be better understood with reference to the subsequent patent claims, description of preferred embodiments, as well as the attached drawings, on which: Fig. 1 is a sketch of a seismic exploration vessel towing an underwater hydrophone cable, Fig. 2 shows, partially in section, an underwater hydrophone cable which includes several electrical devices, Fig. 3 is a block diagram of an embodiment of an underwater power distribution and/or data communication system for use in an underwater cable, Fig. 4 is a block diagram of a another embodiment of an underwater power distribution and/or data communication system for use in an underwater cable, Fig. 5 is a block diagram of a further embodiment of an underwater power distribution and/or data communication system for use in an underwater cable, Fig. 6 is a block diagram of a further embodiment of an underwater power distribution and/or data communication system for use in an underwater cable, Fig. 7 is a block diagram of power conversion circuits in the underwater cable, Fig. 8 is a block diagram of another embodiment of the power conversion circuits in the underwater cable, Fig. 9 is a diagram which is partly a block diagram and partly a connection diagram of a further embodiment of the power conversion circuits in the underwater cable, Fig. 10 is a timing diagram showing examples of timing management of a line for outgoing data and power distribution, and which utilizes the power conversion circuits in fig. 9, Fig. 11 shows an embodiment of a power circuit and decoder for an electrical device, Fig. 12 is an equivalent circuit for an embodiment of power distribution lines, Fig. 13 shows a frequency spectrum for the equivalent circuit shown in fig. 12,

Fig. 14 shows a cross-section of the underwater cable,

Fig. 15 is a longitudinal section through a power distribution line for use in the underwater cable, Fig. 16 shows, seen from above, a coil for use in an underwater cable coupler,

Fig. 17 shows the coil in fig. 16 side view,

Fig. 18 shows the coil in fig. 16 in cross section,

Fig. 19 is a connection/block diagram of coils for use in a coupler in the underwater cable, Fig. 20 partially shows in cross-section a first side of a coil housing for use in a coupler in the underwater cable, Fig. 21 partially shows in cross-section another side of a coil housing for use in a coupler in the underwater cable, Fig. 22 is a cross section of the underwater cable with a coupler and a coil housing arranged inside the coupler, Fig. 23 shows part of a longitudinal section through an embodiment of the underwater cable with a coupler, as well a coil housing arranged inside the coupler, Fig. 24 shows part of a longitudinal section through another embodiment of the underwater cable with a coupler as well as several coil housings arranged inside the coupler, Fig. 25 shows a cross section through another embodiment of the underwater cable with a coupler and a coil housing arranged inside the coupler, Fig. 26 is a connection diagram of a circuit for use in embodiments of electrical devices with a coupler that utilizes several coils, Fig. 27 shows a cross section through another embodiment of the underwater cable with a coupler and a first coil with an integrated core arranged inside the underwater cable's covering, as well as a second coil with an integral core arranged around the underwater cable's covering, Fig. 28 is a connection diagram of circuits that can be used when copying with an integrated core, Figs. 29a-29c are sketches showing magnetic flux lines at an inner integral core configured as shown in Figs. 28, Fig. 30 is a cross section through the underwater cable with another version of a coupler as well as a partially shown wet unit, Fig. 31 is a longitudinal section through the coupler in fig. 30 with a core assembly arranged inside the coupler, Fig. 32 shows part of a longitudinal section through the core assembly in fig. 31, Fig. 33 is a circuit diagram for core assembly circuits which can be used when copying as shown in fig. 30,

Figs. 33A and 33B show magnetic flux lines at the circuit of Figs. 33,

Fig. 34 shows a cross-section of the underwater cable in fig. 30 with a wet unit having a two core assembly arrangement, Figs. 35 and 36 are partly block diagrams and partly circuit diagrams of embodiments of an amplifier,

Fig. 37 is a block diagram of a bit/clock derivation circuit,

Fig. 38 is a partial block diagram and partial connection diagram of an embodiment of a receiver, Fig. 39 is a block diagram of a simplified embodiment of the system for power distribution and/or data communication in underwater cable, Fig. 40 is a partial block diagram and partial connection diagram for an embodiment of an amplifier, Fig. 41 is a detailed block diagram for the amplifier's encoding/decoding circuits, Fig. 42A, 42B is a partial block diagram and partial connection diagram for an embodiment of an electrical device,

Fig. 43 is a circuit diagram for an input data driver circuit,

Fig. 44 is a timing diagram for signals in connection with the transmission of incoming data, Fig. 45 is a detailed block diagram of coding/decoding circuits for the electrical device, Fig. 46 is a block diagram of a load regulation circuit for use in the underwater cable, Fig. 47 is a flow diagram for an embodiment of an apparatus with hierarchical load disconnection, Fig. 48 illustrates the hierarchical load disconnection function that can be assigned to an electrical device, and Fig. 49 shows the switching between primary communication and backup communication.

Description of preferred designs

In fig. 1 and 2, a typical seagoing seismic data recording system 1 is shown which may comprise an exploration vessel 8 which tows one or more underwater hydrophone cables, such as the underwater cable 2. The underwater cable 2 may comprise one or more sections, such as an introduction section and an underwater section 4. The introduction section 3 is connected between the underwater section 4 and electronic equipment 5 at the drying end of the cable. The drying electronics 5 are usually arranged on board the exploration vessel 8 and may include several devices for recording, processing and storing data, as well as control equipment. In certain embodiments, it may be desirable to connect the first and second ends of the underwater section 4 to a first and a second buoy 6, respectively.

The underwater cable 2 can be a continuous hydrophone cable or be disjointed and divided into several cable sections. Fig. 2 shows as an example a part of an underwater cable 2 which can be divided into several cable sections 13 by several hydrophone electronics modules (SEM) 14. In the embodiment shown, the cable sections 13 are arranged alternating with the SEM 14 to form the underwater section 4. SEM 14 can be larger, smaller or have the same cross-section as the cable segments 13.1 a preferred embodiment has the SEM 14 larger cross-sectional extent than the cable sections 13 so that the SEM can accommodate electronic equipment, such as one or more circuit boards. Furthermore, each cable section can comprise an outer sheath 15 attached to water-tight connecting joints which in turn are connected to SEM 14. This configuration enables access for operating the electronics in the individual SEM units. However, the underwater cable 2 need not be limited to this arrangement. The outer jacket 15 can e.g. extend over the entire length of the underwater cable 2 and also enclose the SEM units 14.

As shown in fig. 2, the underwater cable 2 typically comprises several units arranged at selected locations along the cable. Several hydrophones 7 can be selectively arranged along the underwater section 4 for measuring reflected seismic signals. Furthermore, one or more electrical devices 18 can be arranged along the underwater section 4 inside and/or outside the outer sheath 15. When the electrical devices 18 are arranged on the inside of the outer sheath 15, they can be referred to as units 31 in the hydrophone cable. When the electrical devices 18 are alternatively arranged on the outside of the outer casing 15, the electrical devices 18 can be referred to as wet units 30. The wet units 30 are then preferably attached to the underwater cable using one or more wet unit couplers 16.

In the different design examples, the electrical devices can be configured in different ways. A single electrical device 18 can e.g. include a level setting function, depth sensor function, acoustic distance/direction measurement function and/or a compass/direction of movement function, as well as other functions, e.g. inclinometer, gyro, accelerometer, magnetometer, optical distance/direction meter, recovery aids. In certain embodiments, it may also be desirable to divide into one or more functions of two or more electrical devices 18. E.g. level setting devices or so-called birds 10A, compass/direction of movement devices 11 A, as well as acoustic rangefinder devices 12A can be configured as separate units in the hydrophone cable inside the underwater cable 2.1 many embodiments the electrical devices 18 are configured as separate level setting/depth sensing devices or birds 10, compass/direction of movement devices 11, as well as acoustic distance measuring devices 12 and are arranged on the outside of the jacket 15 as wet units 30.

Using known technology, the electrical devices 18 can be used to measure and regulate the shape, direction of movement and configuration of the underwater cable 2.1 many embodiments include the level setting devices, or said birds 10, 10A one or more wings 17 to regulate the immersion depth and/or orientation of the underwater cable 2. The electrical devices 18 typically communicate with and are regulated by the electronic equipment 5 in the cable end on board the exploration vessel 12 over one or more communication channels.

Part I: Power distribution/combination equipment

Reference must now be made to fig. 3, where a power distribution and/or data communication system 20 is shown in block diagram form with the physical connection with the marine seismic data acquisition system in fig. 1 and 2 indicated by dashed lines. In the embodiment shown, the drying electronics 5 comprise a regulation process 21 and a main power supply 22.

The main power supply 22 is preferably connected to a main power line 23

which extends through the lead-in section and then through substantially the entire length of the underwater section 4. Multiple amplifiers 25A-25C may be arranged at selected locations along the length of the underwater cable 2 and may be connected in series or parallel with the main power line 23. As will be discussed throughout description, amplifiers 25A-25C may be implemented in various ways to include several different functions, such as data waveform reformatting, power conversion, control and regulation, error handling and control, power transfer, line drive/receive, line termination, null -digit reception, data/clock synchronization, data connection regulation, data encoding, data decoding, clock cycle recovery, error detection and correction, signal filtering and/or hierarchical load disconnection regulation.

The main power supply 22 can supply either direct current or alternating current to the main power line 23. In the event that the underwater cables 2 extend over long distances, it may be desirable for the main power supply 22 to emit either low-frequency alternating current or direct current power, as well as to use a relatively strong wire cross-section for the main power line 23. Many underwater cables 2 use a main power supply 22 designed to output on the output side a main alternating current signal with a frequency between 1 and 4 kHz to the main power line 23.1 many applications the main power line 23 comprises one or more transmission lines which are at least as strong as 8 gauge wire and which have a length of several thousand meters.

The regulation processor 21 can be connected to the electrical devices 18 in the underwater cable 2 via one or more lead-in lines 26 which can be buffer-connected at each end to interface circuits 27.1 typical designs, the lead-in line can be up to 600 meters in length and normally has no interface to any paralleled or electrical device 18.1 Many of the preferred embodiments allow data to be transmitted over the lead-in section at a rate of up to 64 kbps or higher. Consequently, ordinary line drivers and receivers can be used as interface circuits 27 to form an interface for the regulation processor 21 to the first amplifier 25A. The interface circuit 27 can e.g. include drivers/receivers compatible with EIA RS-422-A (CCITT V. 10) and/or EIA RS-423-A (CCITT V.11) standards.

The amplifiers 25A-25C are arranged alternately with several data and/or power distribution lines 28A-28C to thereby form a data communication channel which runs mainly through the entire underwater cable 2. This data communication channel transmits data between the control processor 21 and several electrical devices 18 at selected locations along the underwater cable. In fig. 3, the electrical devices 18 are shown to be either wet units 30 or units 31 in the hydrophone cable. As previously discussed in connection with fig. 2, the wet units 30 and the units in the hydrophone cable 31 can be configured in different ways, so that they e.g. contains equipment for, a compass/direction of movement function, depth control function, acoustic distance measuring functions and/or other functions.

Each wet unit 30 is preferably connected to one of the data/power distribution lines 28A-28C using a wet unit coupler 16. Similarly, each unit 31 inside the hydrophone cable is preferably connected to one of the data/power distribution lines 28A-28C using a coupler 32 in the hydrophone cable. Reference should again be made to fig. 3, which shows that several copiers 16, 32 are arranged along a data/power distribution line to couple electrical power from the data/power distribution line to the electrical devices 18 (eg wet units 30 and hydrophone units 31). As shown by the dashed lines in fig. 3, the data and/or power distribution lines 28A-28C preferably extend through and have substantially the same extent as each cable section. In many of the preferred embodiments, in addition, the data and/or power distribution lines 28A-28C are connected to the main power line 23 via their respective amplifiers 25A-25C which are placed in each of the hydrophone cables' electronics modules 14.1 Many of the preferred embodiments are the couplers 16, 32 inductive copy. However, any suitable coupling mechanism may be used, including capacitive coupling, ohmic connections and/or optical connections.

In certain embodiments, it may be desirable to include a termination circuit 34 at the outer end of the last data/power distribution line 28C in the underwater cable 2. The termination circuit 34 is preferably configured to provide proper termination of the data/power distribution lines 28A-28C. In alternative embodiments, the termination circuit 34 may also be configured to send synchronization information and/or idle signals along the data/power distribution lines 28A-28C. In many of the preferred embodiments, two oppositely connected Zener diodes (ie a voltage setting circuit as discussed below) may be used to terminate the outgoing data/power distribution lines, while the incoming data/power distribution lines may have a resistive termination.

In fig. 3, the data and/or power distribution lines 28A-28C are shown generally and may comprise any number of physical connections. The distribution lines can be variously configured to include an optical, single-ended and/or balanced electrical connection. Furthermore, the configuration shown in fig. 3 represent a half-duplex or full-duplex system. In the usual way, data transmitted from the electrical devices 18 to the electronic equipment 5 in the drying end of the cable is termed "incoming data", while data transmitted from the drying electronics 5 to the electrical devices 18 can be termed "outgoing data".

In certain embodiments, each data/power distribution line 28A-28C may be constituted

of a single line. For a single line system, time and/or frequency multiplexing for the incoming and outgoing data is preferable. In other embodiments, each data/power distribution line 28A-28C may comprise multiple lines. For a multi-line system, it may be preferable to use a full-duplex communication system where outgoing data is distributed on a different distribution line than the incoming data. Each of the data/power distribution lines 28A-28C can e.g. consists of a double-line system with an incoming data distribution line and an outgoing data distribution line. In such embodiments, it may be desirable to multiplex a power signal either on

the distribution line for incoming data or on the distribution line for outgoing data. Alternatively, each data/power distribution line 28A-28C may comprise three lines where

end data, outgoing data and the power signal are each transmitted on a separate distribution line. Fig. 4 shows an embodiment where the outgoing data and the power signal can be multiplexed together on a single outgoing data and power distribution line 38A-38C, while the incoming data can be distributed on a single incoming data line 39A-39C. In many of the preferred embodiments, the power distribution and/or data communication system 20 can be configured as shown in fig. 4, using a first twisted wire pair for each cable section of the outgoing data/power distribution lines 38A-38C as well as a second twisted wire pair for each cable section of the incoming data distribution lines 39A-39C. The embodiment shown in fig. 4, may be preferable for many applications as this embodiment reduces weight and costs for copper transmission lines while still maintaining a data channel with relatively large bandwidth. Fig. 5 shows an embodiment of the power distribution and/or data communication system 20 with separate power distribution lines for incoming data, outgoing data and power. This configuration can be useful in systems that require the transfer of large amounts of data in both outgoing and incoming directions, where the electrical devices 18 have large power requirements, and/or where the additional weight of a separate power line can be accepted.

Separate power distribution lines can extend either partially or completely through a single cable section. Each cable section can e.g. include two or more power distribution lines. As shown in fig. 5, the cable section A comprises first and second power distribution lines 41, 42. First and second power distribution lines 41, 42 can mainly be arranged through the first and second half of each cable section, respectively. In this configuration, the length of each power distribution line can be reduced by about half the length of a cable section, with amplifiers arranged at each end of the cable section and supplying power to about half of the electrical devices 18 arranged along the cable section. Reducing the length and current requirements of the power distribution lines by half allows for more efficient power transmission as well as a reduction in the size/weight of the dividing wire used in the power distribution lines 41, 42.1 in the case that two or more power distribution lines are used in a single cable section , a termination circuit 44 may be provided to provide correct termination of each power distribution line.

Fig. 6 shows an embodiment of the power and/or data communication system 20, where each amplifier 25A'-25C is preferably designed to amplify data along a primary data channel 48, such as a main data channel used to transmit acoustic hydrophone data to the regulation processor 21. The primary data channel 48 may comprise fiber optic data transmission lines. Each amplifier 25A'-25C may be connected to one or more secondary data/power distribution lines 46, 47 which communicate with some or all of the wet units and internal hydrophone units 30, 31 which are arranged along a cable section 13.1 the shown embodiment, the cable segment 13 be divided so that the amplifiers at each end of the cable section communicate with about half of the wet units 30 and the inner hydrophone units 31 which are arranged along the cable segment 13 and use separate data/power distribution lines.

In the embodiment shown in fig. 6, the secondary data/power distribution lines can distribute data at a relatively slow rate compared to the primary data channel. The secondary data/power distribution lines can e.g. use one or more twisted pairs of copper wires to transmit data and power, as discussed above in connection with the data/power distribution lines shown in fig. 3-6. The amplifiers 25A'-25C may be arranged to perform data link regulation and other data management functions for formatting data transmitted between the primary data channel 48 and the secondary data/power distribution lines 46, 47, depending on the protocols used for the respective channels.

The configuration shown in fig. 6 can be utilized in systems where the primary data channel 48 (e.g. a fiber optic backbone communication channel) has sufficient excess capacity to accommodate additional data to be transmitted

between the drying electronics 5 and the electrical devices 18. An advantage of the system equipment shown in fig. 6 is that the secondary data/power distribution lines can only span a limited distance over all or part of a cable section 13.1 if the length of the secondary data/power distribution lines 46, 47 is

smaller than the cable section, the data rates can consequently be increased and the wire size reduced without adversely affecting the power and data transmission for the electrical devices 18.

In each of the above embodiments of the power and/or data communication system 20, the power is preferably distributed using a hierarchical tree structure where the main power supply 22 forms the roots or base, the main power line 23 forms the trunk, while the data/power distribution lines 28A-28C, 38A -38C, 41, 42, 46, 47 form the branches, and each coupler 16, 32 constitutes a leaf. Each branch can be arranged parallel to the stem and can extend along the cable either in the direction towards the exploration vessel 8 or towards the stern end of the underwater cable 2, depending on the particular design used. When the three-effect structure shown in fig. 3-6 are applied, a) the power and/or data distribution lines can be isolated from each other and applied fault-tolerant properties that maintain communications and/the power distribution even if a fault occurs within a specific cable section, b) the power to the electrical devices is transmitted along a relatively short power distribution line at high frequency, so that the coupling coefficient is improved at a given coil core weight, c) the circuits for transforming the main power signal into a high-frequency alternating power signal are the same circuits that are used to transmit data, and d) the power supply, the circuit boards and the apparatus housing for the present SEM units are shared with the amplifier circuits in order to reduce the weight and complexity that is added to the underwater cable equipment when transmitting operating power to the electrical devices.

Part II: Facilitating the power distribution of the wet units

The above-described power distribution and/or data communication in the system equipment 20 can be facilitated by the addition of a number of elements designed to increase the efficiency of the power transfer to each of the electrical devices and especially to the wet units 30 which may have a low coupling coefficient. In fig. 7, the power conversion circuits for use in the above described embodiments are shown in detail. As discussed above, a main power signal is supplied from the main power source 22. Preferably, the main power signal is a low-frequency alternating current signal or a direct current signal on the main power line 23. The main power signal can be connected to several power conversion circuits 50 in the underwater cable along the main power line 23.

The power distribution and communication system 20 may be configured in various ways to include any number of power conversion circuits located at any number of locations along the submarine cable 2.1 in the event that the submarine cable 2 includes hydrophone electronics modules (SEM) 14, the submarine cable's power conversion circuits may be located within in and/or on the outside of the SEM units, but is preferably arranged inside the SEM units. Furthermore, the underwater cable's power conversion circuits 50 can share some or all of their circuit equipment with the amplifiers 25. By allowing the power conversion circuits to be included in the amplifier circuits and placing the power conversion circuits in the SEM units, the power conversion circuits can share common circuits/circuit boards with the amplifier circuits. Total weight and costs for the power distribution and communication equipment 20 can then be reduced. Alternatively or additionally, some or all of the power conversion circuits may be separate from the amplifier circuits and be arranged along the underwater cable at locations remote from the SEM units.

Each power conversion circuit 50 in the underwater cable is preferably arranged to convert the main power signal on the main power line 23 into a power distribution signal (eg a high frequency alternating current signal). The power distribution signal can then be transferred to each of the electrical devices 18 via a coupler 16, 32, preferably via an induction coil with a core. In some of the preferred embodiments, the power distribution signal is supplied to two or more copies over a data/power distribution line. The power distribution signal can have a frequency between approx. 25 and 400 kHz, as well as preferably between approx. 30 and 300 kHz and even better between approx. 40 and 200 kHz and preferably between approx. 50 and 100 kHz and preferably around 64 kHz. The weight of a core required to achieve a certain level of power transfer efficiency is inversely proportional to the frequency of the power distribution signal. A power distribution signal with a lower frequency requires e.g. a heavier core to provide the same power transfer efficiency as a lighter core used at a higher frequency of the power distribution signal. If the frequency of the power distribution signal was the same as the frequency of the main power signal, e.g. 2 kHz, then the core weight in the coupler would therefore be approx. 32 times heavier than what would be required for a power distribution signal with a frequency of 64 kHz. However, a power signal with a significantly higher frequency can be difficult to maintain with long cable lengths due to losses, e.g. due to load and cable capacitance as well as skin effect in the underwater cable. Furthermore, a significantly higher frequency for the power signal will produce noise which can be difficult to control and exclude from the protected frequency bands used by the hydrophones.

The frequency of the power distribution signal is preferably chosen within the ranges specified above and adapted to the physical wire thickness, length, insulation properties (which determine the capacitance), and the load of the data/power distribution lines, as well as the core weight of the coil. In some of the preferred embodiments, a frequency of around 64 kHz has consequently been found to provide excellent operating characteristics when transmitting power to several wet units 30 on an underwater cable 2.

Although the frequency of the main power signal may vary according to conditions, as indicated above, a seismic submarine cable may use a frequency of about 2 kHz. If a power signal with a frequency of 2 kHz was coupled directly to the wet units via an inductor, for many designs the coupling coefficient would be so low that it would be impractical to power the wet units 30 from the underwater cable 2 without the use of a heavy core. However, by transforming the main power signal into a power distribution signal with a higher frequency at distributed locations inside the underwater cable, it will be possible to efficiently connect power to the wet units 30 even when there is a low coupling coefficient.

As discussed above, transmission of power at a relatively low frequency along the main power line will enable efficient power transmission to the aft end of the underwater cable. Transforming the main power signal with a lower frequency into a power distribution signal with a higher frequency then makes it possible to efficiently distribute power from the main power line to the electrical devices. This is particularly advantageous in the event that the electrical devices are mounted on the outside of the underwater cable and power is inductively or capacitively coupled through the underwater cable's sheath without any physical connections penetrating the cable sheath. This high-frequency signal couples inductive power through the cable sheath much better than a low-frequency signal.

The submarine cable power conversion circuit can be configured in different ways, depending on the operating conditions. If e.g. the main power signal on the main power line is a low-frequency alternating current signal, the submarine cable's power conversion circuit may comprise a cyclo-converter or other device that converts an alternating current signal directly into another alternating current signal. In preferred embodiments, however, it is often desirable and more efficient to first transform the low-frequency alternating current signal on the main power line into a direct current signal and then transform the direct current signal into a high-frequency power distribution signal.

In the configuration shown in fig. 7, each of the underwater cable's power conversion circuits 50 can comprise a first power circuit 51 for converting the main power signal (e.g. either an alternating current signal or a direct current signal) into a regulated direct current signal, as well as another power circuit 52 where conversion of the regulated direct current signal (V2) into a high frequency alternating current signal (V5). In the event that the main power line 23 comprises a direct current power signal, it may be desirable to omit the first power circuit completely. In this embodiment, the main power line 3 will then be directly electrically connected to the second power circuit 52, and V2 will then be equal to the direct current power signal.

In some embodiments, it will be desirable to limit the current emitted from the underwater cable's power conversion circuits. In these embodiments, the current limiting function may be configured in various ways for placement at any location within the submarine cable power conversion circuitry 50 and/or at other locations. In some of the preferred embodiments, the first power circuit 51 comprises a direct current limiter which serves to limit the current supplied to the outgoing data and/or power distribution lines. The second power conversion circuit 52 can receive a carrier clock signal directly or receive a carrier signal after modulation by a possible code circuit 56. If the code circuit 56 is used, then this code circuit will preferably multiplex transfer data to the input 54 for the power carrier signal. The encoder 56 can further utilize one or more clock inputs to synchronize the data/power signals with one or more system clocks. An example of a coding circuit is shown in fig. 9, where the modulation scheme used is binary phase shift keying (BPSK). Accordingly, the encoder 56 can be implemented as an exclusive-OR (XOR) gate 70.

In embodiments of the kind shown in fig. 5 and 6, where power can be distributed on two power distribution lines located in each of two adjacent cable sections, it may be preferable to include a further other power circuit 52A in each of the submarine cable's power conversion circuits 50. This other power circuit 52A can then receive a carrier clock signal directly or after modulation by a possible coding circuit 56A above the carrier input 54A. This further other power circuit 52A can then emit a power and/or data signal to one or more copies and associated electrical devices 18 over another set of power distribution lines.

The amplifier circuits can receive operating voltages from V2 on the first power circuit, from one or more voltage regulators and/or from one or more DC/DC converters. In the event that the amplifiers require several DC voltages, one or more DC/DC converters 53 may optionally be arranged to produce one or more DC voltages V3, V4, or the first power circuit 51 may produce one or more DC voltages V3A, V4A.

The underwater cable's power conversion circuit 50 may optionally comprise one or more transformers 55 to isolate the power conversion circuit 50 from the data/power distribution lines. In some of the preferred embodiments, the transformer 55 can also be used to increase the voltage on the data/power distribution line to thereby facilitate the power transmission along the cable section 13. It can e.g. be desirable to increase the voltage to between 10 and 400 volts, and preferably between 15 and 200 volts, and even better between 30 and 100 volts and most preferably to around 42 volts.

As the wire size of the data/power distribution lines becomes smaller (eg, as the wire gauge increases), the voltage on the data/power distribution lines is preferably increased to achieve the same efficiency. However, there will be a lower limit to how thin wire can be used before the voltage increases so much that the power distribution signal begins to be coupled to the rest of the underwater cable's electronics (especially into the hydrophone circuits). In some of the preferred embodiments, a voltage of about 42 volts on the data/power distribution lines with a wire gauge of 26 AWG will provide sufficient power transfer for up to about 3 watts, preferably around 1.4 watts to each of two devices, without adversely affecting other electronic equipment in the underwater cable 2, while maintaining a high degree of efficiency for the power transmission.

The wire gauge for the main power line and for the data/power distribution lines can

determined in different ways. In certain embodiments, e.g. the wire gauge on the main power line be between 2 and 14 AWG, preferably between 4 and 12 AWG, and even more preferably between 6 and 10 AWG and most preferably around 8 AWG. In contrast, the wire gauge for the data/power lines may be between 20 and 36 AWG, and preferably between 22 and 32 AWG, and even more preferably between 24 and 30 AWG and most preferably around 26 AWG.

The underwater cable's power conversion circuits can be located at any location within the power distribution and/or data communication equipment 20.1 certain designs, it may be desirable to distribute the underwater cable's power conversion circuits 50 along a cable section in the underwater cable 2. A power conversion circuit can e.g. be located in each amplifier and/or each coupler.

In certain embodiments, placement of a power conversion circuit 50 for the underwater cable in each coupler 16, 32 can reduce the noise in the underwater cable to a minimum. Fig. 8 shows an embodiment where each coupler comprises a power conversion circuit 50 for the underwater cable. In the embodiment shown in fig. 8, the couplers (e.g. first couplers 16', 32') can be configured as a three-inductor coupler, where the power input data and output data are coupled to an electrical device 18 that utilizes three different coils. The underwater cable's power conversion circuits 50 in the coupler 16', 32' can receive a clock signal from the clock generator circuit 59 from the carrier input 54A. In this embodiment, the carrier frequency for the power transfer is preferably produced by the clock generator circuit and can be independent of the data transfer rate for incoming and outgoing data. The clock generator circuit 59 may be constituted by any suitable circuit, such as a crystal oscillator.

In the embodiment shown in fig. 8, the couplers (e.g. second copy 16", 32") can be configured as a two-inductor coupler, where e.g. power and outgoing data can be connected to an electrical device 18 using a first coil, and incoming data can be connected to an electrical device 18 using a second coil. The carrier input 54 (not shown in Fig. 8) of the submarine cable power conversion circuits 50 in the copier 16", 32" can receive a signal directly from the outgoing data line or indirectly through an encoder 56 (not shown). If data from the outgoing data line is to be encoded above the encoder 56, a carrier clock signal may be applied to the encoder 56 from any suitable source, such as another clock generator circuit 59A (not shown).

Distribution of the underwater cable's power conversion circuits 50 in different places until each of the electrical devices 18 has an advantage in that the amount of noise produced by the power transmission to the electrical devices 18 can be reduced to a minimum. The configurations shown in fig. 8 is, however, less preferred in many circumstances, due to space limitations in certain coupler designs and which can make it difficult to include power conversion circuits in the couplers without the use of specially adapted integrated circuits.

Fig. 9 shows an embodiment of the underwater cable's power conversion circuits 50.1 in this embodiment, the data input shown is gate controlled by XOR gate 70 with the power carrier clock. The output from the XOR gate can constitute the input signal to the power conversion circuits 50.1 embodiments where data is not modulated on the power signal, the unmodulated carrier signal can be supplied as an input signal directly to the power conversion circuits.

The modulated or unmodulated carrier output from the XOR gate 70 is preferably used as an input signal to an inverting buffer 72 and a non-inverting buffer 71 arranged inside the power conversion circuits 50.1 embodiments where data is not applied in multiplex on the data/power distribution lines, the possible data input and the XOR gate 70 is omitted as the power carrier clock outputs the input signal directly to the inverting buffer 72 and the non-inverting buffer 71. The output signals from the buffers 71, 72 control the switching of the transistors 73, 74, which in turn regulate the output data and/or the power distribution signal on the data/power distribution lines.

Fig. 10 shows a time chart for the work function for an embodiment of the circuit shown in fig. 9.1 in the embodiment shown, the power carrier clock has a frequency of 64 kHz (fig. 10a). In preferred embodiments, the output data (eg, data modulated by the XOR gate 70) may be distributed at a lower frequency than the power carrier due to capacitive loading and other noise considerations. It was found that modulating data on the carrier using a data rate different from the carrier sequence band significantly improved system reliability, particularly in the case where data and power were transmitted along a data/power distribution line. Data can therefore be transmitted at a rate of about half the carrier frequency, and preferably about a quarter of the carrier frequency and even more preferably about an eighth of the carrier frequency and most preferably about a sixteenth of the carrier frequency or less. When data and power are transmitted on the same line, transmission of a data signal will result in a significantly lower bit rate than the center carrier frequency for a power signal, resulting in higher power transmission efficiencies while maintaining reliable communications. In the embodiment shown, data is transmitted at a rate of 4 kbps (Fig. 10b), which is one sixteenth of the carrier frequency of 64 kHz.

The power transfer efficiencies are affected by a load resistance at the point along the data/power distribution lines where the power is taken out as well as by the capacitance of the line and the bandwidth of the signal. Due to capacitive coupling and relatively high load resistance on the data/power distribution lines, the RC time constant of the outgoing link can be relatively high. Accordingly, high power transfer efficiencies and reliable data transfers can be achieved in those cases where the ratio between the data transfer rate and the power transfer frequency is kept at about 1:2 or less, and preferably about 1:4 or less, and even more preferably about 1:8 or less and very preferably around 1:16 or less.

A technique for transmitting a data signal and a power signal on the same line is binary phase shift keying (BPSK). As shown in fig. 9, the BPSK encoder may simply be an XOR gate, such as XOR gate 70. An example timing diagram for the output of XOR gate 70 is shown in FIG. 10c. As shown in fig. 10c, a change in the output data signal corresponds to a phase change of the BPSK signal. Fig. 10d shows an example of the output data/power signal delivered to the power distribution line or lines in each cable section after being coded by the BPSK encoder 70. In some preferred embodiments, the transformer 55 steps up the output voltage on the data/power the distribution lines to about 42 V.

From fig. 11 it appears that when each of the electrical devices 18 is inductively coupled to the data/power distribution lines, the electrical devices preferably comprise a power circuit 60 for converting the alternating current signal received from the couplers 16, 32 into a direct current signal. Although the power circuit of the electrical devices can be configured in different ways, the power circuit 60 in the embodiment shown in fig. 11 a resonant capacitor 65, a full-wave rectifier bridge 61 for outputting a rectified signal, a low-pass filter (e.g. a smoothing capacitor 64) for filtering the rectified signal into a direct current signal, and a voltage regulator (not shown) for regulating the DC signal to a desired voltage level. One or more DC/DC converters (not shown) may optionally be present to provide DC outputs with different voltages.

As shown in fig. 11, when data is modulated onto the data/power distribution lines, it may be desirable to separate the outgoing data signal from the power signal in the electrical device, e.g. by using voltage dividers 62 and comparators 63. The resonant capacitor 65 produces square-shaped voltage waves on the input side of the full-wave rectifier bridge. These waves followed by the comparator produce a very reliable recovery of the data waveform. The output data signal can then be transmitted to data communication circuits, such as data encoders and decoders.

As discussed above, it may be appropriate to transmit a power distribution signal on the data/power distribution lines using an elevated voltage to increase the efficiency of the power transmission to the electrical devices, and in particular for inductive power supply to the wet units 30. However, this power transmission can produce noise which may have an adverse effect on

other equipment in the underwater cable, such as the hydrophones 7.

It has been found that by limiting the bandwidth of the frequency spectrum of the power distribution signal on the data/power distribution lines to occupy a band different from, and preferably spaced from, the frequency band used by the hydrophones, significant improvements to the hydrophone signal/noise can be achieved - ratio is achieved. Until now, this has been difficult to achieve while maintaining sufficient data communication bandwidth and power transmission with a high degree of efficiency. However, it has been found that these problems can be overcome by limiting the length of the data/power distribution lines and by applying a distributed filter along these lines.

When each cable section is limited to about 500 meters or less, and preferably to 400 meters or less, and even more preferably to about 300 meters or less and most preferably to about 200 meters or less, it is possible to process each of the data/power the distribution lines as an element with a concentrated parameter and create an electric wave filter by utilizing elements distributed along the cable section. Best results are obtained when the wavelength portion of the power distribution line is preferably no more than one-tenth of the power carrier signal's wavelength. In the event that the data/power distribution lines are 200 meters long, it will e.g. it may be preferable that the power carrier signal has a frequency that is not higher than about 100 kHz. Under these conditions, a distributed filter can be constructed which

limits the frequency spectrum of the power signal to lie outside the protected hydrophone bands.

The longer the wire length, the lower the allowable frequency will be to utilize a distributed filter technique. Lower frequencies have the undesirable effect of requiring larger and heavier coil cores to achieve sufficient power transfer.

The power/data distribution lines, driver circuits, coupler transformers and the electronics of the electrical devices are preferably operated as a matched power transmission circuit. Fig. 12 shows a Thevenin equivalent circuit for the embodiment of a power transfer circuit 79 which includes the distributed filter technique, as discussed above. The equivalent circuit for an embodiment of an output or driver section of the submarine cable power conversion circuit 50 is implemented as a block 80.1 the embodiment shown, the Thevenin equivalent circuit for the submarine cable power conversion driver circuits 80 comprises a voltage source V,n, an inductor L1, a resistor R1 and a capacitor C1. The inductor L1 and the capacitor C1 are discrete components that can be used to adjust and improve the filter properties of the distributed filter. The resistance R1 is made up of the internal resistance in the inductor L1 and the other losses in the power conversion circuit 50. The equivalent circuit for an embodiment of the power distribution line is indicated as a block 81 and comprises series connection of R2 and L2 followed by a parallel connection of C2 and R3. The equivalent circuit for the parallel-connected replicas (it is assumed that all replicas are inductive) is indicated at block 82 which shows a resistor R4 connected in parallel with a series circuit comprising a resistor R5 and an inductor L2, a mutual inductance M23, an inductor L3 and a series resistor R6. The load comprises the resonant capacitor C3 and resistor R7. (see fig. 12.)

An important feature of the power transfer circuit which roughly corresponds to the Thevenin equivalent circuit shown in Fig. 12, is the configuration of the power transfer circuit to be in resonance at the carrier frequency of the power distribution signal, as well as the configuration of the circuit to form a filter, preferably a bandpass filter, centered at the carrier frequency. An example of the frequency response for the power transmission circuit which is approximately represented by fig. 12, is shown in fig. 13. As shown in fig. 13, it is possible by adjusting the concentrated and distributed parameters of each data/power distribution line, as well as the values of the discrete components L1, C1, L2, M23, L3, C3 to obtain a distributed bandpass filter with a frequency band centered around the power distribution signal's carrier frequency (e.g. 64 kHz), while maintaining a sufficiently sharp cutoff to avoid coupling any significant energy from the power distribution signal into the hydrophones' operating frequency band.

The outer sheath 15 of the underwater cable 2 can be a plastic sheath with a thickness of approximately 3 mm. Consequently, there can be a large core gap in the transformers which are made up of copy 16 and wet units 30. A normal transformer has a coupling coefficient of around 0.98 or better. However, transformers used to couple the data/power distribution lines to the wet units 30 may have a coupling coefficient as low as 0.1 or lower. It was found that if the data/power distribution lines are designed as an electrical wave filter, e.g. a three-resonator bandpass filter, it would be possible to include the transformer in the filter and thus increase the power transfer efficiencies for the transfer between the data/power distribution lines and the wet units 30. As shown in fig. 13, the bandpass filter can be in three sections, e.g. have a center frequency of 64 kHz and a bilateral bandwidth of 8 kHz. In this configuration, the data/power distribution lines will transmit +4 kbps BPSK data on a 64 kHz carrier without distortion.

The right part of fig. 13 shows an example of a frequency band in which several hydrogens work (often referred to as the forbidden bands). The prohibited bands can be configured in different ways to include one or more frequency bands, preferably separated and/or at a distance from the frequency bands of the distribution lines. In one embodiment, the prohibited bands reserved for hydrophone operation are integer multiples of 128 kHz with a 500 Hz guard band. In such a system, it is therefore desirable to configure the frequency band for the power distribution signal and the data signal so that the frequency bands used for hydrophone operation are avoided. The bandpass filter in three sections may be designed to reduce the signal energy in these bands to a predetermined low level.

Wire used for the data/power distribution lines in each cable section is preferably a low-loss cable with a loss factor that is kept within low tolerances. This low-loss cable is preferably designed to have a capacitance determined to tune the power transfer circuit, to tune the filter's frequency band, and to minimize power loss in the data/power distribution lines due to capacitive coupling to other parts of the underwater cable 2.

The underwater cable 2 can usually be filled with a lossy dielectric material. A lossy dielectric material means that the material has a loss factor of around 0.01 or greater, including e.g. a loss factor of about 0.1 or greater. The lossy dielectric material may be a petroleum-based material, such as an isoparaffin solution (eg, ordinary paraffin), a wax, a liquid, and/or a solid plastic material. If the lossy dielectric material is a liquid, it is preferable that an outer sheath 15 is arranged around the underwater cable 2 to accommodate the liquid. If the lossy dielectric material is a solid, the outer jacket can be formed from this solid material and the solid material can then extend along the entire underwater cable 2.

The lossy dielectric material is usually used in an underwater cable to provide buoyancy. Any liquid, solid or semi-solid lossy dielectric material that is less dense than seawater will be sufficient to set the buoyancy for the underwater cable 2. A problem with distributing power through a lossy dielectric material is that the lossy dielectric has a high relative permittivity . An isoparaffin solution can e.g. have a relative permittivity of approx. 3. By filling the underwater cable with a lossy dielectric with a relative permittivity of e.g. 0.1, 1.0, 2.0, 3.0, 10.0 or more, the capacitance of the data/power distribution lines can be changed. Investigations have shown that even with excellent insulation applied to the power distribution line, the loss due to lossy dielectric can be far too high, especially when twisted wire pairs, high voltages and high frequencies are used. In many embodiments, it has been found that the presence of the lossy dielectric reduced the efficiency of the data/power distribution lines to an inoperable level.

Investigations have shown that this problem can be overcome by placing an outer plastic sheath or cover around the insulated power distribution line. When e.g. the data/power distribution lines are made up of insulated twisted wire pairs, an outer cover can be arranged around the insulated twisted pairs. In fig. 14 and 15, the underwater cable 2 is shown placed under water 86 and filled with a lossy dielectric material 87. In certain embodiments, the underwater cable 2 may comprise a number of supporting or stiffening cable units 84, the fiber optic cable is called 85 and/or electrical cable units 89 (e.g. main power line 23). In addition to an incoming data distribution line 43 and an outgoing data/power distribution line 38, 41, 42, 46. In certain embodiments, the bracing cable units 84 may be designed to transmit main power

to replace and/or supplement the main power line 23.1 preferred designs are a

outer jacket or an outer cover 83 (preferably of plastic material) arranged around the power/data transmission lines, which is formed from a twisted pair of wires where each wire is itself insulated by the use of a cover 88.

In some of the preferred embodiments, it may be that the outer jacket 83 is not placed around the data lines, such as the incoming data distribution line 43. In many applications, there may be no need for a low-loss cable or a coated cable on the incoming data distribution lines, as these lines is usually terminated with a low resistance and because the capacitance usually does not need to be regulated to the same level as when power is to be distributed. A considerable reduction in costs can thus be achieved while maintaining highly reliable data transmissions on the incoming data distribution lines.

Fig. 15 shows a longitudinal section through the data/power distribution lines 38, 41, 42, 46, including the outer sheath 83. In preferred embodiments, the data/power distribution lines with an outer sheath 83 have a loss factor D that is less than approx. 0.01 and preferably less than about 0.008 and preferably less than about 0.006 and even more preferably less than about 0.004 and most preferably about 0.002 or less when surrounded by the lossy dielectric material.

The coupling loss coefficient for the data/power distribution lines can also be determined so that the distribution filter described above produces the desired filtering properties, as specification of insulation thickness also helps determine the capacitance. The power distribution lines are usually specified in henry per meter and farad per meters. To obtain a highly reliable filter, in some of the preferred embodiments the cable capacitance can be regulated to within a tolerance of ±5% so that the power transfer circuit remains tuned and the filter remains centered on the carrier frequency of the power distribution signal.

Experiments have shown that distribution of power to the electrical devices 18 over twisted pairs of wires arranged in an outer sheath is extremely effective, and particularly when the power distribution signal comprises relatively high voltages and relatively high frequencies. It has been found that the outer sheath 83 which is arranged over the twisted pair of wires which make up the power distribution line, remarkably increases the efficiency of the power transmission, especially when the data/power distribution lines form a tuned power transmission circuit. The data/power distribution lines are preferably configured to include both an outer jacket 83 and insulation 88 on the twisted pairs of wires themselves. Furthermore, the outer sheath 83 is preferably a low-loss cable sheath, so that each power/data distribution line receives a low loss factor D as discussed above. Generally, sheathed and insulated, low-loss twisted wires have not been used to distribute power to electrical devices in underwater cables.

Extensive problems exist for inductive replicas arranged in underwater cables. The underwater cable 2 has e.g. limited cross-section to accommodate the inductive coils due to numerous carriers, electrical and optical cable assemblies, as well as electrical devices 18 disposed within the underwater cable 2. Although certain coil core materials are preferable from an electromagnetic perspective, these core materials have been found to have brittleness that prevents operation. A brittle core can cause reliability problems when the underwater cable 2 is taken up and wound up over one or more steel rollers 9 on the exploration vessel 8. Furthermore, alignment problems often occur when the couplers are assembled and dismantled in the field. The core in the underwater cable can e.g. come out of alignment relative to the core of the wet unit. An alignment problem can often greatly reduce the coupling coefficient of the coupler. When more than one coil is assigned to a particular coupler, crosstalk between the coils has also been found to be a problem. Even a single coil can also cause coupling into the hydrophone lines and adversely affect other underwater cable systems. Substantial research effort has consequently been directed towards producing highly efficient inductive replicas which are suitable for use in the transmission of operating power to electrical devices 18 arranged in seismic underwater cables.

In fig. 16-18 shows a first embodiment of an inductive coupling coil 90 for use in the couplers. As shown in fig. 18, the inductive coupling coil 90 has a substantially triangular cross-section as well as a winding 91 wound around at least a portion of the substantially triangular core 92. In certain embodiments, it may be desirable to apply a cut-off portion 96 to one or more locations of the substantially triangular core 92.

The substantially triangular core 92 preferably has first, second and third substantially planar side surfaces 93, 94 and 95. The first planar side surface may be considerably larger than the second and third planar side surfaces. The first planar side surface 93 is preferably arranged facing the outside of the underwater cable 2 with contact with the outer sheath 15. The coupling coil 90 is preferably arranged with a longitudinal axis 97 aligned parallel to the longitudinal axis of the underwater cable 2, so that the first essentially planar side surface is placed in the longitudinal direction along the underwater cable 2.1 design examples, it may be desirable for the first side surface 93 to have a rounded shape, so that this first side surface has a contour with approximately the same curvature as the inside of the underwater cable 2. Furthermore, the second and third side surfaces 94, 95 may be mainly flat.

The winding direction 98 and the design of the coils are preferably precisely specified. Accurate winding of the coils can reduce crosstalk to a minimum, in the event that two or more coils are placed very close to each other, increase the efficiency of the power transmission, and reduce inductive coupling to the hydrophone's electromagnetic system to a minimum. These precisely executed windings can be of particular importance in seismic underwater cables where operating power is inductively coupled to the wet units 30.

Considerable research effort has been directed toward determining an optimal inductor/coil core configuration. In fig. 17 paint spot 99 indicates the coil orientation with respect to the cross-section A-A shown in fig. 18. Fig. 18 shows a winding direction 98 for the coils. In certain embodiments, the winding direction is preferably the same for all coils (either clockwise or counter-clockwise relative to the paint spot 99, thereby facilitating correct installation.

As shown in fig. 19, it may be desirable to arrange two or more coils close to each other. In this embodiment, e.g. coil A 90A is used for transferring outgoing data/power to a wet unit 30, while coil B 90B e.g. can be used for the transmission of incoming data from a wet unit 30. The paint spot 99 can be used as a reference point to indicate that it is difficult for the windings in the coils A and B to be laid in opposite directions to reduce crosstalk. The windings in coil A 90A are e.g. laid in a clockwise direction, while the windings in coil B 90B are laid in an anti-clockwise direction.

In the preferred embodiments, each coupler 16, 32 includes an outgoing data/power tap line 110 to connect the coupler to the outgoing data/power distribution line 38, as well as an incoming data tap line 111 for the purpose of connecting the coupler 16, 32 to the distribution line 39 for input data. Each drain line can have a larger, smaller or the same wire cross-section as an assigned distribution line. In certain embodiments, the tap lines 110, 111 have a wire size that is smaller than the wire size of the distribution lines 38, 39. In preferred embodiments, the wire gauge may differ by 1, 2 or more AWG values. In some of the more preferred embodiments, each drain line has a smaller dimension than a connected distribution line.

The drain line 111 for incoming data is preferably connected to lead wire wound around the core of the coil B 90B and consists of blue wire BLU. Although the windings in coil B 90B may be configured in various ways, the winding wire is preferably a wire with a wire gauge of 26 AWG or larger, preferably 28 AWG or larger, and more preferably 30 AWG or larger, and most preferably about 32 AWG. The number of turns of blue wire BLU can be differently configured to adapt to the frequency of the data transmitted over this coil. In some of the preferred embodiments where the input data is transmitted at 64 kHz, the blue lead wire BLU preferably has about 353 turns.

The drain line 110 for outgoing data/power is preferably connected to lead wire wound around the core of coil A 90A and consists of red wire RED. Although the windings in coil A 90A may be configured in various ways, the winding wire is preferably a wire gauge wire of 26 AWG or larger, preferably 28 AWG or larger, and most preferably around 30 AWG. The number of turns of red wire RED can be configured differently to adapt to the frequency of data/power transmitted through this coil. In some of the preferred embodiments, the red lead wire RED has about 158 turns.

Under certain circumstances, the power transmitted to the wet units 30 may still have a connection into the data distribution line. However, it was found that this problem can be overcome by inserting a counter coil 12 (green lead wire GRN) electrically connected between the blue coil and the input data drain line 111, and physically wound around the core of coil A 90A. Although the counter coil may be configured in various ways, the winding wire is preferably wire gauge wire of 26 AWG or larger and preferably 28 AWG or larger, and preferably about 30 AWG. The number of turns of green wire GRN can be adapted to the expected electromagnetic coupling between the two signals on coil A 90A and coil B 90B respectively, but is preferably around 21 turns. Typically, a counter coil is achieved where each coupler comprises a first coil connected to the first line (e.g. a distribution line for outgoing data and/or power) as well as a second and a third coil connected to another line (e.g. a distribution line for incoming data), where the first and second coils are located at a distance from each other (usually wound around separate coil cores) and where the first and third coils are located close to each other (usually wound around the same core) for regulation of crosstalk between the first and second coil, as well as between the first and second line.

In many designs, the cores of the coils can have high brittleness. Accordingly, it was found that the reliability of the underwater cable could be greatly improved by arranging the coils (eg coils 90A, 90B) in a coil housing. In fig. 20, which shows a cross-sectional side elevation of part of the underwater cable 2, the coil A 90A is shown arranged in a first pocket 121 of a coil housing 120. In a similar way, fig. 21 a turned cross-sectional side elevation of the same part of the underwater cable 2, with the coil B 90B arranged in another pocket 122 of the coil housing 120. The housing 120 is preferably formed of a substantially rigid material, such as a plastic material or a metal alloy which has sufficient structural strength to protect the coils 90A, 90B.

The pockets 121, 122 can be designed in different ways. In some embodiments, the pockets 121, 122 are located with a fixed fitting against the coils 90A, 90B. In certain preferred embodiments, however, the pockets are somewhat larger than the coils 90A, 90B to allow some bending of the housing 120 without adversely affecting the reliability of the coils 90A, 90B. The pockets may be sealed off from the rest of the underwater cable. Furthermore, the pockets may be filled with any cushioning material, such as foam material, high viscosity oil, grease, gel and/or other spongy substances. It may be desirable to arrange the damping material so that it presses and/or positions the coils against the outer covering 15 of the underwater cable in order to reduce the gap between the coils 90A, 90B and respectively the coils 129 and 130 to a minimum. In embodiments where the underwater cable 2 is filled with a liquid lossy dielectric material 87 (e.g. kerosene), the pockets 121, 122 can be in fluid communication with this flowing lossy dielectric material 87, or preferably be sealed from this lossy dielectric material.

When the underwater cable 2 is coiled up on the exploration vessel 8 and over one or more steel rollers, very large forces will be exerted on the underwater cable 2. The coil housing 120 which is arranged around the coils 90A, 90B can then protect the brittle core 92 from bursting. In certain embodiments, the coils 90A, 90B can be designed to float inside their respective pockets, 121 and 122, respectively. By floating, it is meant that the coils are not rigidly connected to the housing 120. Even if the external forces are sufficient to affect the housing 120 to bending, in these embodiments the core 92 will remain unaffected due to the fact that the core floats (that is, it is not firmly anchored) within the pockets 121, 122 in the coil housing 120.

Fig. 22 shows a cross-section through the underwater cable 2, with the sheath 15, the coil housing 120 and a wet unit casing 128. First and second coils 129, 130 are arranged in the wet unit casing 128 directly opposite each of the coils 90A, 90B which are located in the coil housing 120. The first coil 129 preferably comprises a winding 127 arranged around a core 126. In a similar way, the other coil 130 comprises a winding 125 arranged around a core 124. In some of the preferred embodiments, the cores 124, 126 are elongated and arranged in the longitudinal direction of the underwater cable in a similar way to the coils 90A, 90B.

Additional details of the wet unit housing, coil housing 120 and coupler 116 are set forth in one or more of the following US provisional applications, namely, No. 60/004,203, filed September 22, 1995, 60/004,209, filed September 22, 1995, 60/005,500, filed Sep. 22, 1995, 60/0004,493, filed Sep. 22, 1995, 60/004,494, filed Sep. 22, 1995, as well as in the co-pending international application entitled Underwater Cable Arrangement by Andre W. Olivier, Brien G. Rau, and Robert E. Rouquette, filed on the same day as the present international application and is hereby incorporated by reference.

The coils 90A, 90B are mutually separated by a radial angle <)> 123. Electrically, an angle of 180 degrees provides the best noise immunity between the coils. In certain embodiments that include an odd number of bracing and/or power cables, such as the five cables 84 shown in FIG. 22, however, another angle may be preferred. In the embodiment shown, an angle of 144 degrees is used and has been found to provide the best noise immunity, providing the highest coupling coefficients and/or minimum core sizes when used together with five stiffener and/or power cables 84. In that case the wet unit case comprises two halves , an angle of approx. 144 degrees between the coils enable both coils to be arranged in the same half of the wet unit housing.

A problem with the known common core configurations is that the coils cannot tolerate any significant deviation in the alignment between the coils in the underwater cable 2 and the coils in the wet unit casing 128. In experiments, it has been found that a coil will usually be able to tolerate a misalignment equal to the width of the pole face as well as a displacement in the longitudinal direction which is equal to the longitudinal extent of the polar surface. The geometry of the coils shown in fig. 16-18 are then indicated to have a relatively large outer side 93 to allow a certain degree of misalignment, e.g. up to 1.25 cm or more, without the circuit that supplies the coils with power being tuned. The wet units can then be equipped with copiers that can maintain a precision of plus or minus 1.25 cm. In this configuration, the inductances will not change by more than about 6%, and the distributed filters and the tuned circuit can then be maintained within the operating tolerances. The power transfer circuit can be designed so that when the inductances change by about 6%, the total filter tuning will only change by approx. 3% (that is, one over the square root of LC). As the power transmission circuit is a resonant circuit, the waveforms will change without the power being transmitted to the loads normally being reduced. The relatively wide and mainly flat coil configurations and especially the triangular coils have thus been shown to have excellent operational reliability and power transfer efficiencies.

A longitudinal section through the underwater cable 2 with a single coil housing 122 arranged in the coupler 16 is shown in fig. 23. However, the couplers 16 are not limited to this embodiment and may be configured in various ways to contain any number of coil housings. Fig. 24 thus shows e.g. a longitudinal section through a coupler 16 with several coil housings 122A, 122B assigned to a wet unit casing 128. Fig. 23 and 24 show one or more chambers 131 inside the wet unit casing 128, and which can contain electronic equipment for operating the electrical devices 18.

Fig. 25 shows another embodiment of the coupler 16, where the wet unit casing 128 contains several coils 129A-129G. As with previously shown embodiments, the coil 129A-129G may comprise cores, respectively 129A-129G, and windings, respectively 127A-127G. Any number of coils may be used, eg three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen or more. In the embodiment shown, seven coils are arranged in the wet unit casing 128.

The embodiment shown in fig. 25 can be advantageous from the fact that the sheath 128 can be connected to the underwater cable 2 with any circumferential orientation without significantly affecting the efficiency of the power transfer between the underwater cable and the wet unit 30. This arrangement can be particularly appropriate in the case that the coils 126A -126G inside the wet unit 30 can be rotated in relation to the underwater cable 2. In order to achieve complete rotational position tolerance, the coils in the casing 128 are preferably arranged so that the mutual distance between neighboring coils (e.g. between the coil 129A and 129B) is smaller than the width of the pole face of the coils 90A, 90B in the circumferential direction.

In the event that multiple coils are used, it may be desirable to provide a semi-solid or fully solid wet unit sleeve 128 in the area near the coils 129A-129G to provide additional support.

The electrical connection between coils 129A-129G in FIG. 25 can be configured in different ways. Fig. 26 shows e.g. an embodiment where all electric coils are connected to a full-wave rectifier bridge 135 with several inputs and which includes diodes D1A-D1G, D2A-D2G, D3 and D4. A filter capacitor 131 is connected to the output of this multi-input full-wave rectifier bridge 135. A direct voltage output 128 from the filter capacitor 131 is transferred, e.g. preferably to voltage regulators (not shown) to provide DC power to associated wet unit electronics. Output data may be extracted using a voltage divider 133 and a comparator 134. Input data may be coupled to said multiple coils 129A-129G by providing multiple secondary windings 139A-139G.

In fig. 27 shows an alternative embodiment of the coupler 16, where the underwater cable 2 e.g. comprises an inner integrated core 140 arranged in the outer jacket 15, while the electrical device 18 e.g. comprises an outer integrated core 147 arranged around the outer sheath 15. The outer integrated core 147 can be arranged in a wet unit casing 128 to shock-absorb and protect this outer integrated core 147 inside the coupler 16. The inner integrated core 140 preferably comprises a hollow passage 141 with e.g. several optical fibers and electrical wires 141A which are passed through the passage.

Inner and outer integrated cores 140, 147 may each comprise several projecting sections around which several coils may be wound. In the embodiment shown in fig. 27, the inner integrated core 140 comprises four windings 146A-146D arranged about four projecting sections 142A-142D which project outwardly from and are integral with the inner integrated core 140. Similarly, the outer integrated core 147 shown in fig. 27 four windings 145A-145D arranged around four projecting sections 148A-148D, which can project inwardly from and are integral with the outer integral core 147. The inner and outer projecting sections 142A/148A, 142B/148B, 142C/148C , 142D/148D lie directly opposite each other and each form its own polar surfaces A-D.

In the embodiments shown in fig. 27, the projecting sections 142A-142D on the inner integrated core and/or the projecting sections 148A-148D on the outer integrated core can be made with a curved surface to adapt to the curvature of the underwater cable 2 and thereby also increase the coupling coefficient. The projecting parts can also be made in the form of a truncated triangle with a curved outer side in contact with the outer sheath 15 of the underwater cable 2.

In many applications, the coils shown in fig. 27 be more advantageous than previously used coils, due to the fact that the copter's geometric design allows a relatively large pole surface. The achieved flux line configuration will then ensure excellent coupling between the coils in the underwater cable 2 and the coils in the wet units 18.

The integrated core 140 may comprise any number of projection sections (eg from 2 to 20) depending on the number of wires to be wound around each projection section. In the event that the integrated core has only a single lead wire wound around each projecting section, the integrated cores may utilize any even number of projecting sections. In the event that each winding 145A-145D, 146A-146D comprises two or more wires, it is advantageous to arrange four, eight, sixteen or more projecting sections around the integrated core.

An integrated core with four projecting sections will e.g. allow up to three wires to be wound around each of the projecting sections in a manner that cancels the mutual coupling between the windings, so that multiple signals can be transmitted using a single integral core.

Fig. 28 shows e.g. a wiring diagram for a configuration with three leads and four pole faces, and which is configured to cancel and/regulate the mutual inductances between the leads. In the embodiment shown, the windings in the connection part of the underwater cable 2 and the connection part in the wet unit 30 for the coupler 16 are the same for each pole surface. The wire A can e.g. have turns on the first and fourth pole surface wound in a first direction (either clockwise or counter-clockwise) as well as turns on the second and third pole surface wound in the opposite direction, both in the underwater cable section and in the wet unit section of the coupler 16. Lead wire B may have turns on pole surface 1 and 2 wound in a first direction, as well as gains on polish surface 3 and 4 wound in the opposite direction. In this way, the configuration of the turns for lead wire B can exclude any coupling of signal B to lead wire A. Similarly, lead wire C can have turns on pole surfaces 1 and 3 wound in a first direction and turns on pole surfaces 2 and 4 wound in the opposite direction. In this way, the gain configuration for lead C will preclude any coupling of signal C to leads A and B. The winding directions allow for mutually orthogonal signals where half of the gains will add signals and half of the gains will subtract signals with respect to any other winding except the intended signal transmitting winding. No voltage from signal A will thus appear on wires B and C, no voltage from signal A will appear on wires A and C, and no voltage from signal C will appear on wires A and B. The signals A, B and C can thus be used same and/or different voltage levels as well as the same and/or different number of wins without affecting each other. A signal applied to wire A in the underwater cable will then appear on wire A in the coupler without any corresponding voltage appearing on wires B and C. The magnetic flux lines produced by the windings A, B and C are shown respectively in fig. 29A-29C.

Examples of winding configurations which may be suitable for use in the embodiment shown in fig. 28, is summarized in table 1, where the letters A, B and C represent windings for the different wire leads A, B and C in a first direction, while A, B and C represent windings for the respective wire leads A, B, C in the opposite direction.

The above winding configurations shown in fig. 29A-29C as well as in table 1 are given as an example. A winding opposite to that shown for each pole face can be used for any given wire direction. In this way, there can be eight different possible winding permutations. In table 1, e.g. the winding direction for wire A must be inverted as A A A A. This inverted wire winding direction for wire A can be used in coordination with the wire winding directions for wire wires B and C shown in table 1 or their inverse winding pattern. Similarly, the wire winding direction for wire B can be inverted as B B B B and used together with the indicated wire winding directions for wire wires A and C or their inverse winding pattern. In general, each of the wire winding directions for the wire leads A, B and C can be inverted individually or in combination, so that eight possible combinations can occur in operation.

The designs with integrated cores for the coupler are very advantageous and represent a significant advance when it comes to achieving efficient coupling between a wet unit 30 and an underwater cable 2.1 the embodiment shown, the wire leads for different signals can be placed very close to each other and share a single core while mutual inductive coupling between the different signals is substantially avoided. The signal/noise ratio for the underwater cable's power distribution and/or data communication system 20 is thereby improved at the same time as the efficiency of the power transmission is increased. Due to the fact that the copter's geometric design allows for a relatively large pole surface, the coupling between the inner and outer core will also be considerably improved.

The coupler with integrated core can be adapted to facilitate coupling with any designs of the submarine cable's power distribution and/or data communication system 20. Signal A can e.g. be the main power signal from the main power line or the power distribution signal from one of the data/power distribution lines, signal B can be the outgoing data signal from one of the outgoing data distribution lines, and signal C can be the incoming data signal from the wet units 31 to the underwater cable's incoming data distribution lines.

Even further designs are also possible. In the four-pole design, it can e.g. be desirable to use only one wire A to transfer e.g. power and outgoing data, while wire B is used to transmit incoming data and wire C is omitted entirely.

Designs with an integrated core make it possible to reduce the length of the coils in the axial direction compared to the coils shown in fig. 16-18. The length of the coil shown in fig. 27 can e.g. be less than 7 cm in the axial direction, which is preferably less than 5 cm and rather less than 4 cm, and most preferably less than 3 cm. A significant reduction of the length in the axial direction helps to improve the coils' reliability and reduce the cases where the coils break due to bending of the underwater cable 2 when it is passed over the rollers 9.

The couplers with an integrated core can be particularly advantageous in the event that the underwater cable 2 has a main power line 23 comprising two or more conductors. In one embodiment, the main power line 23 comprises four main power cables which are laid directly through the integrated core 140, as e.g. is shown by the main power cables 84A-84D in fig. 27.1 these designs, the cables 84A-84D can also have a bracing function in addition to their power distribution function. Due to the high coupling coefficient and the geometry of this particular coupler, it may be possible to eliminate the high frequency data/power distribution lines as well as the power conversion circuits in certain designs. In these embodiments, the main power line 23 is connected directly to the coupler 16 by routing one or more main power cables through the integrated core 140. The main power cables 84A-84D can e.g. transmit four main power signals with alternating polarity. The thread winding direction for e.g. Lead wire C can then be obtained by simply passing a main power line 23 composed of four conductors of alternating polarity through the integral core 140 (eg, between the projecting sections 142A-142D and/or the windings 146A-146D, as shown at the main power cables 84A-84D in Fig. 27). In this embodiment, signal C in fig. 28 be the signal derived directly from the main power line.

The current direction in the main power conductors 84A-84C preferably alternates for each successive conductor around the integrated core, so that winding directions C C C C or the inverse winding pattern are created. With this connection arrangement, the main power from the main power line 23 (distributed on the main power conductors 84A-84C) can then be distributed directly from the main power line 23 into the wet units without an intermediate secondary power distribution line and an AC/AC converter. However, this method is less preferable for many designs, as the integrated cores are relatively heavy.

Fig. 30-34 shows yet another embodiment of a coupler which is particularly suitable when the coils in the wet unit can be rotated in relation to the underwater cable. A coupler 300 comprises a mainly cylindrical housing 301 with a number of parallel bores. A central bore 302 accommodates lines for electrical power and data. Several bores 303 distributed along the circumference, preferably around three, accommodate strain relief elements. Several coil cavities, preferably approx. six, are distributed along the circumference and preferably arranged in pairs between the strain relief elements. In a preferred embodiment, each coil cavity 304 comprises a blind end bore with a coil 305 arranged therein. Although a symmetrical arrangement of boreholes is preferable, other arrangements can also be used when adapting to different underwater cable structures.

The coupler housing 301 preferably has a tight fit inside the cable sheath 306. Longitudinal grooves 307 along the outside of the coupler 300 allow cable-loading fluid to flow past the coupler. A groove sleeve 308, which is divided into two halves, is attached around the sheath 306 and the coupler housing 301. A wet unit 309 is preferably rotatably attached to the cable by means of a collar 310, which fits into and slides in the groove of the sleeve 308 Hinge connection 311 and a locking assembly 312 which may have a quick release pin enables the collar to be split at the locking pin, allowing removal of the collar and wet assembly 309 from the cable and track sleeve 308.

As shown in fig. 31, each coil cavity 304 in the housing 301 preferably has an open end 313 and a blind end 314 and accommodates a coil assembly 305. As shown in fig. 32, the coil assembly 305 comprises a magnetic core 315, which preferably comprises a ferrite rod, although other magnetic materials can also be used. The magnetic core 315 has a high relative permittivity, which is preferably above 6000 and most preferably above 6500 or more. In the preferred embodiment, the magnetic core 315 comprises a ferrite rod embedded in a sleeve 316, which is preferably slightly longer than the magnetic core 315. Shock absorbers, such as elastomeric end dampers 317, hold the core 315 in place longitudinally and dampen the coil assembly 305 against shock. The sleeve 316 comprises several pairs of circumferential chambers 318, preferably about 4. A sleeve support ring 319 is held in place between the chambers in each pair. The support rings 319 are preferably made of an elastic material with an outer diameter slightly larger than the inner diameter of the coil cavity 304. The support rings 319 keep the core 315 centered in the cavity 304, protect the core 315 against bending, and also protect the core 315 against shock loads in transverse the direction. An end cap 320, which is preferably watertight, holds the coil assembly 305 in place in the cavity 304. The shock absorbers 317 may be in contact with the inside of the end cap 320 and the blind end 314. An O-ring 321 mounted in a circumferential table in the end cap 320 seals the cavity 304 against fluid ingress. Outer wires 322A-B connect the coil windings to the submarine cable lines for power, outgoing data and incoming data. The outer wires 322A-B preferably extend through an end cap 320 and form a connection with the coil windings 331 A-B at the connections 334. A strain relief 323 can protrude from the outside of the end cap 320 to prevent wire damage. The end cap 320 is preferably provided with an extraction loop 324 to facilitate removal of the coil assembly 305 from the cavity 304.

In fig. 32, it is shown that each coil assembly 305 preferably comprises multiple windings 331 A-B, 332A-B at separate locations 325, 326 along the core 315. A circumferential channel 327 may be formed between the pairs of chambers 318 at each end of the casing 316. Each channel 327 serves as a coil form to hold the windings 331A-B, 332A-B in place. An A coil winding 331A, 332A and a B coil winding 331B, 332B are wound inside each channel 327. The A coil windings 331 A, 332A couple output power and/or data to the wet units 309. The B coil windings 331B, 332B couple data from the wet unit 309 to the incoming data lines inside the cable. The B-coil windings 331B, 332B can also be used to couple outgoing data to the devices on the cable when operated in the back-up communication mode, as will be discussed more fully below.

The windings may be connected in any suitable manner. As shown schematically in fig. 33 is e.g. The A-coil windings on the core 305 are electrically connected in a series-promoting arrangement as indicated by the dot marking. The A-windings for each core are connected in parallel with the A-windings for the upper cores. The B-windings on each core, on the other hand, are connected in opposing series arrangement to reduce the mutual inductance between the A-windings and the B-windings and thereby reduce crosstalk to a minimum. The B-windings on each core are connected in series with the B-windings for the other cores.

Reference must now be made to fig. 33A and 33B, where the reduction of crosstalk is illustrated by the flux paths produced by each set of windings. In fig. 33A, it is shown that the series-interacting A-coil windings 331A and 332A on a coupler 315 produce a flux which also passes through the series-interacting A-coil windings 331A' and 332A' on a similar nearby core 329 in the wet unit along a flux path 340. The outer ends of the cores 315, 329 thus act as pole faces 343, 344 for the A windings' service path. As shown in fig. 33B, the series opposing B coil windings 331B, 332B on the coupler core 315 produce a flux which also passes through the series opposing B coil actions 331B' and 332B' in the wet unit core 329 along the flux paths 341 and 342.1 in addition to the pole faces 343, 344 at the outer ends of the cores, a third pole face is formed between the windings 331A and 331B for the B winding's flux path. Because the flux produced by the A windings runs in the same direction through the cores, no net voltage will be induced in the series opposing B windings. Because the flux produced by the B windings is oppositely directed in each half of the cores, conversely no net voltage will be induced in the series cooperating A windings. In this way, crosstalk between the incoming and outgoing lines will be reduced to a minimum. It will be clear that one set of windings belongs to two pole planes, that two sets of windings lead to three pole planes, as shown in fig. 33B, and that three winning sets result in four poker faces, as indicated in fig. 28, and that in general N sets of windings lead to N + 1 pole surfaces.

Reference should again be made to fig. 33 which shows that a tuning capacitor 328 can be connected in parallel with the A-coil circuit to tune a resonant circuit which is formed together with the capacitance in the output data line and the inductance in the A-coil circuit. Tuning the resonant circuit increases the power transfer to the wet unit. In a most preferred embodiment for use with a 200 meter underwater cable section accommodating two wet units, the total inductance of the A windings would be about 0.246 mH and the tuning capacitance would be about 25.1 nF to transfer about 1.5 W of power to each wet unit at 64 kHz. A total inductance of around 3.09 mH is preferred for the B windings for efficient transmission of incoming data to the research vessel at 32 kbps.

In fig. 30 it is shown that only one coil assembly 329 is located in the wet unit 309 near the coupler 300. The coil assembly 329 in the wet unit is preferably of similar design to each of the coil assemblies 305 in the coupler. The core in the wet unit arranged parallel to the core 315 in the coupler 300 with the positions of the two windings separated in the radial direction with little, or preferably no displacement in the longitudinal direction. In this way, the inductive coupling between the windings in the coupler 300 and the windings in the wet unit 309 is improved.

In the particular geometric design of the coupler 300 in fig. 30, the coupling between the coupler and the wet unit 309 will vary as the wet unit 309 is rotated around the cable. Maximum coupling is achieved when the axis of the core 329 in the wet unit 309 is equidistant from the neighboring coupler cores 305 and not radially aligned with a relief element bore 304, as indicated by a first radius 335 in fig. 30. Minimal coupling occurs when the cable is rotated relative to the wet unit 309, as indicated by the dashed line, to a position where the core 329 of the wet unit 309 lies along the same radius 336 as the bore 303 for a strain relief element.

If space is available in wet unit 309, coupler 300, or both,

additional cores can be installed to further increase the maximum coupling coefficient. As shown in the embodiment in fig. 34, can e.g. a pair of identical cores 330 in the wet unit 309 improve the coupling rather than the embodiment in fig. 30.

Part III: Data communication distributed in general

Usually, in the past, the communications between the electrical devices 18 and the drying electronics 5 have taken place over one or more communication lines which extend mainly through the entire length of the underwater cable

2. However, this configuration may be unsatisfactory when electrical power is distributed over the same lines as data. Intrusion of seawater can e.g. misalignment of the entire communication channel and cable loss can make communication and power transmission difficult over long distances. Consequently, power transmission and communications will be difficult or impossible using previously known configurations.

Another aspect of the present invention relates to improving the responsiveness and reliability of the communication channels, including the data/power distribution lines between the search vessel 8 and the electrical devices 18. As can be seen from fig. 3-6, the underwater cable 2 may comprise a communication system with a control processor 21 which controls the communications to and from one or more communication channels. As shown in fig. 3-6, each communication channel can comprise several amplifiers 25 for sending/receiving data. Each communication channel can e.g. comprise a first group of amplifiers arranged at selected locations along the underwater channel 2. The communication channel may be configured in various ways to include any number of amplifiers located at any number of suitable locations within the underwater cable 2.1 preferred embodiments the underwater cable comprises multiple amplifiers spread along the underwater cable and placed at approximately the same distance from each other.

In the event that the underwater cable 2 comprises hydrophone cable electronics modules (SEM) 14, the amplifiers can be arranged inside and/or on the outside of the SEM units, but are preferably arranged inside the different SEM units. The amplifiers may be arranged alternately with the data/power distribution lines to form a data communication channel. In this arrangement, the data communication channel is divided into sections by the amplifiers. Furthermore, the amplifiers are spaced apart at various locations along the underwater cable and serve to transmit data between the electrical devices 18 and the control processor 21 on the exploration vessel 8.1 preferred embodiments, any number of replicas 16, 32 can be arranged along each section of the communication channel to couple electrical signals on the data/power distribution lines to an electrical device 18 located near a coupler. Each section of the communication channel can e.g. include one, two, three, four, five, six, seven, eight, nine, ten, or more copies. When the amplifiers are arranged in the SEM units, the sections of the data communication may coincide with the cable sections. In many preferred embodiments, each communication section comprises two separate replicas arranged between successive amplifiers. More than two copies can also be inserted between successive amplifiers. The two copies transfer data and/or power from the data and/or power distribution lines to the assigned electrical device 18.

It has been found that the buffering effect provided by one or more amplifiers limits the effect of any loss of an electrical device along a particular communication channel section to the tuning of that particular section of the data communication channel alone. Power and/or the data transmission to electrical devices 18 along other communication channel sections can consequently persist. Furthermore, retransmission of message signals at a predetermined level of the amplifier at one end of the detuned section may be sufficient to overcome the detuning effects and allow reliable communications to electrical devices located along the submarine cable 2 after a detuned section.

In some of the preferred embodiments, the amplifiers comprise encoders, decoders and/or control circuits 154 for the data connection. (See fig. 35-36). The circuits 154 may be configured in various ways. In certain embodiments, e.g. the circuits 154 take random samples of data received from the receivers 152,153 and send out the sensed sample data in synchronism with one or more system clock signals. The system clock signal can be derived from data on a separate line or from data on the incoming and/or outgoing data distribution lines. If a clock signal is to be derived from data on the incoming and/or outgoing data distribution lines, the clock signal can be derived with or without recovery of data bit information. By e.g. feeding either the incoming or the outgoing data into an edge detector and then into a phase-locked loop (PLL), a clock cycle can be extracted from the transmitted data signal. The extracted system clock can be used to recover bit information by demodulating the relevant data and then re-modulating this data before transmission to an output driver circuit. Alternatively, the system clock can be used to simply sample data received from the receiver and retransmit this data in synchronism with the system clock without demodulation.

In certain of the preferred embodiments, the output data received by the amplifier 25 is sampled to derive a system clock which is then used to demodulate the output data to recover output data bit information. The outgoing data is then preferably modulated again using the system clock. Bit recovery can also be performed in a similar way on the incoming data. Furthermore, the amplifiers 25 can sample the input data from the receiver 153 using a derived input data clock, and then retransmit the input data in synchronism with the system clock derived from the output data.

In certain embodiments, the amplifiers 25 may also include additional circuits to perform various connection regulation functions, such as error detection and/or error correction, as well as connection control functions. Furthermore, it may be desirable to include a microprocessor or other suitable control circuits in the amplifiers 25.1 these designs, it may be desirable to perform bit recycling for e.g. to achieve error correction and/or error detection for each segment of the data communication channel. The arrangement of control circuits for the data connection in each amplifier can be advantageous in applications where it is desirable to create error detection and/or error correction for the individual data/power distribution lines.

In configurations that have a separate communication channel between the dry-end electronics 5 and the electricals 18, amplifiers that include data link regulation are often preferred to a lesser extent because of the additional latency introduced by the packetization, error correction and/or error detection that takes place in each amplifier .

The amplifiers 25 which comprise coding/decoding and/or data connection control circuits can be designed in different ways. The amplifiers 25 can e.g. be configured to operate as a full-duplex and/or half-duplex communication channel over one or more signal distribution lines (eg one or more twisted pair connections). Fig. 35 shows an exemplary embodiment of an amplifier 25 designed for communication over a single line, while Fig. 36 shows an exemplary embodiment of an amplifier 25 configured for full-duplex communication over two lines. In those cases where half-duplex communications are used, the amplifier is preferably configured to operate over a single line. Where full-duplex communications are used, the amplifier is preferably configured to operate over two or more distribution lines.

In fig. 35 there is shown an embodiment of the amplifier 25 configured for half-duplex communications. The amplifier 25 then comprises a drive circuit 150 to drive input data and/or power on a first adjacent input/output data/power distribution line, as well as a receiver 152 to receive data from the first adjacent input/output data/power distribution line. Similarly, an output driver circuit 150 may be included to drive data and/or power on another adjacent input/output data/power distribution line, and a receiver 153 may be included to receive data from the other adjacent input/output data /power distribution line.

Fig. 36 is of a similar nature to fig. 35 except that in fig. 36 the drivers 150, 151 for the amplifier 25 connected and configured for full-plex communications.

In some of the preferred embodiments of the power distribution and/or data communication system 20, the equipment works in a full-plex system and comprises a communication channel for incoming data with several amplifiers which are alternately arranged with several distribution lines for the incoming data, as well as a communication channel for outgoing data with several amplifiers arranged alternately with several distribution lines for outgoing data. Each data communication channel connects the control processor 21 to the electrical devices 18. In some of the preferred embodiments, the data/power distribution lines and the output data distribution lines are the same lines.

In the embodiments shown in fig. 35 and 36, power from the underwater power conversion circuits may be transmitted on a separate power distribution line or the power may be combined with data and transmitted over some of the drivers 151 and/or 150 in a similar manner as discussed above in connection with the power distribution circuits. In embodiments having a separate power distribution line, the underwater power conversion circuit 50 may include an isolator to provide a power carrier clock to transfer power at the power carrier clock frequency to one or more of the data/power distribution lines. In the event that power and data are to be transmitted on the same line, it may be desirable to let the second power circuit 52 be included in one or more of the driver circuits 150,151.

In some of the preferred embodiments, power and data are transmitted by means of an outgoing data driver 151. An example of such an embodiment is shown in fig. 4.1 this embodiment, the power transmission is maintained by sending out idle signals when no data is to be transmitted. The electrical devices 18 extract electrical power from the data signals and idle signals to provide operating power and power for charging any batteries.

As discussed above, the amplifiers 25 can operate to create a simple buffer function by reshaping the signals emitted from the amplifier to have predetermined voltage levels. In these simple buffer arrangements, the receivers 152, 153 are preferably connected directly to the respective drivers 151, 150.

In this simple buffer configuration, no encoder/decoder and/or link control circuitry need be included in the amplifiers 25. The simple buffer configuration can be advantageous in that the amplifiers work to regulate the biasing of the power/data distribution lines, while introducing very little waiting time between the exploration vessel 8 and the electrical devices 18. However, the simple buffer arrangement may be less preferable due to the bias along the underwater cable, as will be discussed below.

A first embodiment of the encoder/decoder and/or connection control circuits 154 for use in the power distribution and/or data communication equipment 20 is shown in fig. 37.1 the embodiment shown includes only coding/decoding circuits in the amplifiers, the connection control circuits for data being completely omitted. The connection regulation circuits for data (e.g. HDLC circuits) can of course still be used in each electrical device 30, 31 as well as in the drying electronics 5.

The decoding circuit 173 for the input data and the decoding circuit 170 for the output data may include such circuits as a phase-locked loop for recovering a clock and logic circuits for utilizing the clock to recover more data bits. In a similar way, the coding circuits for the incoming data 172 as well as for the incoming data 171 can comprise circuits for modulating data on a clock carrier frequency. As will be discussed in more detail below, in certain embodiments it may be desirable to derive a carrier frequency CLK 74 from output data by using a decoding circuit 170 and then use this clock to synchronize the incoming output data over the encoding circuits 171,172.

The decoding circuits 170, 173 can be one and the same circuit or different circuits depending on the modulation scheme used on the incoming data channels and the outgoing data channels. In some of the preferred embodiments, the decoding circuitry 170 may be configured for 4 kbps BPSK while the decoding circuitry 175 may be configured for 32 kbps Manchester encoding.

The above-mentioned amplifiers can be used in any of the versions of the power distribution and/or data communication equipment 20. An amplifier that is optimally designed for use together with the power distribution and/or data communication equipment 20 shown in fig. 6, preferably includes circuitry to form interfaces to both primary and secondary data communication channels. In this embodiment of the amplifier 25, it is often desirable to include data link regulation in each amplifier for packaging and unpacking of data that is transmitted to and received from the drying electronics 5 using the primary data channel.

Fig. 38 shows an exemplary embodiment of the amplifier 25 designed to cooperate with the embodiment of the power distribution and/or data communication equipment 20 shown in fig. 6.1 fig. 38 it is shown that the amplifier circuit 25 has a primary data channel and a secondary data/power distribution channel. The secondary data/power distribution channel may comprise one or more encoders, decoders and associated drivers and receivers, as well as power conversion circuits in the underwater cable in a similar manner as discussed above. The incoming and outgoing data is preferably packed and unpacked by CPU and/or data link control circuits 175 for transmission over a primary data channel, such as a fiber optic network in the submarine cable. The amplifier 25 may include one or more drivers, receivers, encoders and/or decoders 180-187 to facilitate communications over the primary data channel. Furthermore, the CPU and/or the data connection control circuits 175 can be arranged to digitize signals from one or more hydrophones (not shown) e.g. along each adjacent cable section. As will be discussed in connection with fig. 40, where drivers 151 are arranged to transmit both data and power, it may further be advantageous to include drivers 151 in the power conversion circuits.

Part IV: Synchronization of incoming/outgoing data

A common problem that occurs when introducing bit and/or clock recovery circuits in the amplifiers 25 is that additional waiting time can be introduced. This latency often results from carrier recovery loops in the decoders which introduce a time delay with respect to data. When a wet unit starts to react, this unit can be expected to send out a long block warning, the length of which depends on the number of decoders between the electrical device in question and the drying electronics 5. Furthermore, it is required of the electrical devices 18 at the aft end of the underwater cable 2 to use a long block warning of at least 3-4 bit times for each amplifier between the electrical device and the regulation processor 21. A long waiting time can thus exist before the regulation processor 21 receives a reaction to a previously sent request.

This problem can be overcome by using a continuously active synchronous transmission protocol. This protocol can be particularly effective in the event that data communications between the search vessel 8 and the electrical devices 18 comprise regulation and data messages with a relatively short message length. A continuously active, synchronous transmission protocol can help to reduce the part of the bandwidth for the communication channel that is devoted to origination and synchronization bit units. In certain embodiments of the continuously active, synchronous protocol, the incoming and outgoing data communication channels are kept continuously active, e.g. by means of continuous transmission of idle signals when no data is available.

In a full-duplex synchronized system, the control processor 21 preferably keeps the output data and/or the power line continuously active by e.g. to send instructions to one or more of the electrical devices or also zero/idle signals. Similarly, the incoming connection can be kept continuously active by sending either messages or an idle pattern. The idle pattern for the incoming connection may be produced by the last amplifier in an incoming connection, by the termination circuit 34, by means of a random or non-random signal generator and/or by noise produced by the rear section of the data communication channel. In some of the preferred embodiments, the idle signals are generated by noise on the very back section of the data communication channel, and which are then amplified and sent out by the last amplifier. Power can be distributed on the same line as data or on a separate line with or without an effect tree structure. In some of the preferred embodiments, however, the power tree structure is superimposed on the synchronized amplifier structure in a complementary manner, so that the outgoing data and the power transmission utilize the same distribution line.

A problem when creating a synchronous communication protocol in a long underwater cable is that different degrees of bias between the electrical devices along the underwater cable 2 add to time uncertainties. Electrical devices 18 near the search vessel 8 can receive messages and respond quickly. However, as the electrical devices 18 are further and further away from the search vessel, the electrical devices 18 may be exposed to different degrees of delay. A response from an electrical device arranged near the aft end of the underwater cable may consequently be biased in relation to a response from electrical devices near the exploration vessel 8. The degree of bias may increase with increasing cable length. This can be particularly problematic when it is desired to utilize a single cable architecture adapted to different cable lengths. Varying degrees of skew may also make it necessary to reduce the bandwidth of the data channel in order to achieve reliable data and power transmission while allowing varying cable lengths and varying degrees of skew.

In some of the preferred embodiments, the above problems can be overcome by using a clock derived from decoded data and/or a carrier along

a first data and/or power distribution line to synchronize data and/or a carrier along the same or another data and/or power distribution line. In the embodiment shown in fig. 4, it can e.g. be desirable to utilize a carrier clock derived from data on the outgoing data on the outgoing data and/or power distribution lines 38A-38C to synchronize incoming data on the incoming data distribution lines 39a-39C. In different embodiments, a synchronization clock can be supplied by any of the components of the present underwater power distribution and/or data communication equipment 20, but preferably a clock that is written from the dry-end electronics 5 or from electronics arranged towards the aft end of the underwater cable 2.

Fig. 39 shows a simplified block diagram which shows one of the preferred embodiments of the synchronized time relationship between the different function blocks in a full-duplex communication system with incoming data synchronized with outgoing data. In some of the preferred embodiments, auxiliary circuits for creating timing can be included in the amplifiers 25 and in the electrical devices 18 to determine the incoming data and/or the carrier clock to have an exact time relationship with the outgoing data and/or the carrier clock. Reference must now be made to the execution which

is shown in fig. 39, where the carrier clock derived from the output data by decoder 170 can be used by encoder 172 to synchronize input data. This synchronization can occur both in the amplifiers 25 and in the electrical devices 18. The carrier clock can also be used to synchronize data encoded by the encoder 171

and distributed to the rear cable section. In this way, each of the amplifiers and each of the electrical devices can be locked in a precise time context, so that there is no need to create time management when a response from an electrical device 18 is to be sent out.

The special nature of the timing may vary depending on the modulation scheme used and the special circuits used to implement the synchronization. In preferred embodiments, the incoming data/carrier clock is usually delayed by a quarter carrier period relative to the outgoing data/carrier clock. This synchronized design has the advantage that it sets the bandwidth of the incoming data to a maximum, while at the same time any time delay is reduced to a minimum, regardless of the number of amplifiers along the underwater cable 2.

In embodiments utilizing the synchronized scheme, each encoder connected to the incoming data distribution line (including the encoders in the electrical devices 18) preferably has a carrier phase that is slaved to a carrier clock on a corresponding outgoing data distribution line. Each amplifier 25 and each of the electrical devices 18 connected to a particular data and/or power distribution line is preferably configured to include a carrier recovery loop as well as a bit time recovery loop which is continuously locked. Delay time or bias in the time relationship between the outgoing signal and the incoming signal varies depending on the distance from the amplifier along a specific power/data distribution line, but is usually only a fraction of a bit time (the biggest delay can e.g. be about 3 microseconds in one of the preferred embodiments where the distribution lines are limited to about 200 meters). Any bias on a particular distribution line can be accommodated by a minor adjustment of the timing recovery circuit, which can typically be achieved within a quarter of a bit time.

An important advantage of synchronized recovery loops is that each amplifier

not only reshapes the data signal, but also completely removes any build-up of timing uncertainties due to bias. Further cable sections and/or communication channel sections can thus be added without rebuilding any of the components in the power distribution and/or data communication equipment 20.

Figs. 40 and 41 show detailed connection/block diagrams of driver/receivers and synchronized circuits with time recovery loops in the amplifiers 25, while fig. 42A, 42B, 43 and 44 show detailed connection/block diagrams for drivers/receivers as well as synchronized circuits with recovery loops in the electrical devices 18.

In fig. 40, an amplifier circuit 25 is shown which comprises an outgoing data receiving circuit 152 for receiving signals from outgoing data and/or power distribution lines. In preferred embodiments, the receiver circuit 152 for outgoing data provides correct termination for the distribution lines for the outgoing data and/or power as well as reshapes the data signal for input to the decoding circuit 170. The receiver circuit 152 for outgoing data may comprise a comparator 189 and a load adjustment circuit 188. The load adjustment circuit 188 is discussed in more detail below.

The decoding circuit 170 preferably forms part of the encoding/decoding and/or connection control circuit 154 (shown in detail in Fig. 41). As discussed above, the circuit 154 can be configured in different ways, but preferably comprises decoding circuit 170 for outgoing data, coding circuit 171 for outgoing data, decoding circuit 173 for incoming data, and decoding circuit 172 for incoming data, as shown in fig. 40 and 41.

In some of the preferred embodiments, the output data decoded by the decoding circuit 170 is preferably re-encoded by the encoding circuit 171 and then output through the output data and power distribution line driver 151. As discussed above with reference to fig. 7 and 9, where data and power are connected to the same lines, it may be desirable to configure the driver 151 as part of the submarine cable's power conversion circuit 50.

The amplifier circuit 25 can also comprise a receiver circuit 153 for incoming data and which is arranged to receive signals from the distribution lines for incoming data and/or power. In preferred embodiments, the receiver circuit 153 for incoming data can create correct termination for the distribution lines for incoming data and/or power, as well as redesign the data signal for input to the decoding circuit 173. The receiver circuit 153 for incoming data preferably comprises a band rejection filter to reduce crosstalk from the outgoing data lines or coils to the incoming data lines or coils. In the preferred embodiment, the input data demodulated and/or sampled by the decoding circuit 173 is preferably then re-modulated and/or subjected to a new sampling process by the encoding circuit 172. The newly modulated and/or newly sampled signal is then rejected as an output signal through the driver circuit 150 for incoming data.

Fig. 41 shows a detailed block diagram of one of the preferred embodiments of the encoder, decoder and/or connection control circuits 154.1 fig. 41 it is shown that outgoing data from the receiver 152 constitute input signals to a first digital phase-locked loop (DPLL) 156. The first DPLL 156 comprises an edge detector 150, phase detector 157, filter 158 and a numerically controlled oscillator (NCO) 159. The phase detector 157 emits one or more signals indicating whether the phase output from NCO 159 occurs earlier, later or simultaneously with the phase of the signal detected by the edge detector 155. The phase detector 157 may be created by an XOR gate or other suitable circuits. The filter 158 is used to create low-pass filtering to screen out all transient abnormalities such as is produced by noise. The filter 158 may be created as a divide-by-N counter or other suitable circuitry. The adjusted output from NCO 159 is then heard as input back to phase detector 157 to complete the loop. The output of DPLL 156 (denoted as BPSK CLK) may be configured to be any multiple of the carrier frequency, but is preferably equal to the carrier frequency (fco) of the output data received from receiver 152.

A phase demodulator 160 can be included where it is desired to receive data bit information. The phase demodulator 160 preferably receives output data from the receiver 152. The output from the demodulator 160 preferably forms input to another digital phase-locked loop 164 to recover a bit rate clock. The bit rate clock has the same data rate as the outgoing data which in some of the preferred embodiments is set to a rate of 4 kbps. The second DPLL 164 comprises a bit edge detector 155', a phase detector 157', a filter 158' and an NCO 159' in a similar arrangement to the first DPLL 156.

The bit rate clock from the second DPLL 164 and the demodulated data from the phase demodulator 160 constitute input to the sampling unit 161. This sampling unit 161 samples the demodulated data in synchronism with the bit rate clock. The output of the sampling unit is data that does not return to zero

(NRZ). This NRZ data constitutes the input signal to a dual-phase modulator 163 and is used to modulate the BPSK clock from the first DPLL 156. In this way, outgoing data on a subsequent communication channel section can be transmitted in syn-

chronism with a clock signal derived from data transmitted in the immediately preceding communication channel section. The output from the double-phase modulator 163 then preferably constitutes the output signal to the driver 151 for outgoing data for transmission over the subsequent cable section.

The department for incoming data in fig. 41 shows a sampling unit/phase demodulator 166 for sampling the incoming data in conjunction with a Manchester clock (MANCLK) which is an equal multiple of, or preferably equal to, the carrier frequency (fee) of the incoming data. In the embodiment shown, the incoming data is sampled at the carrier frequency (sweep) for this data. The Manchester clock MANCLK is generated by a third DPLL 165. This third DPLL 165 comprises a bit edge detector 155", a phase detector 157", a filter 158", as well as an NCO 159" in a similar arrangement as in the first DPLL 156.

Sampling unit 167 receives on its input side Manchester data from sampling unit 166 and resamples this data in synchronism with the BPSK CLK output of first DPLL 156. A divide-by-N circuit, such as a counter, may be used to divide the BPSK CLK signal down to the carrier frequency of the incoming data, which in the preferred embodiment is 32 kHz. The sampling unit 167 uses the divided BPSK CLK signal for sampling incoming data. In this way, the incoming data can be synchronized with the outgoing data without it being necessary to demodulate the incoming data.

Figs. 42A and 42B show a block diagram of a preferred embodiment of the electrical devices 18 (e.g. a wet unit 30 or a hydrophone cable unit 31) for use in embodiments of the underwater cable's power distribution and/or data communication equipment 20. Reference should now be made to fig. . 42A and 42B, where the electrical device 18 can receive power at the power source 200 from a battery, a combined input data/power line, an output data/power line and/or a line dedicated exclusively to power distribution. In the embodiment shown, the power source 200 receives power from a combined distribution line for outgoing data and power.

The power source 200 may be configured in various ways to constitute any circuit capable of converting received power into regulated equal-to-peak power. In the embodiment shown, the received power from the distribution lines for outgoing data and power is preferably alternating current power. As discussed above in connection with fig. 11, a full-wave rectifier bridge 61 can be used to rectify the alternating current signal, while a capacitor 64 can be used to smooth the rectified signal into a direct current power signal (Vpwr). A power limiter 201 is preferably arranged to limit the amount of power a device can extract from the cable. A power limiter can also be used to limit the power that is extracted from the batteries. The direct current power signal can then e.g. regulated by e.g. a DC voltage regulator or other converter 210 from DC level to DC level to provide operating power to circuits contained in the electrical devices 18.

In certain embodiments, it may be desirable to let the electrical devices 18 include one or more batteries 212.1 certain of the preferred embodiments, where batteries are included, the batteries can be recharged via the battery charger 211. If batteries are included, these batteries can emit operating power in that case power is not available from the underwater cable 2. The batteries 212 can be switched to an operating mode of e.g. a diode or an electronic switch. If an electronic switch 221 is used, the battery charging circuit 211 preferably comprises a low-voltage detector which emits a low-voltage signal to the microprocessor 204. The microprocessor 204 can then activate the electronic switch 221 in response to the low-voltage detection signal. Alternatively, the microprocessor 204 can detect a low voltage directly across the A/D 214. In yet other embodiments, the electronic switch 221 can be controlled directly by the voltage detector 211, e.g. as a reaction to a voltage that is too low.

In some of the preferred embodiments, the A/D converter 214 receives a voltage from the input of the voltage regulators 210 as well as a separate voltage from the output of the voltage regulators 210. In this way, the microprocessor 214 can monitor the voltage received from the underwater cable 2 as well as the voltage emitted from the batteries (when these are present and active). The voltage regulators 210 preferably have a cut-down mode that can be used to isolate the input from the output when the power is insufficient on the input side of the voltage regulators 210. The microprocessor 204 can regulate one or more controlled circuits 205 based on the voltage values received by the A/D converter 214.

The A/D converter 214 may be integrated with the microprocessor 204, such as e.g. with the Motorola 68HC11, or be a separate unit connected to the microprocessor 204. As discussed in more detail below, the A/D converter 214 can be used by the microprocessor 204 to initiate various actions by one or more controlled circuits 205 arranged inside the electrical devices 18.

A reset circuit 213 can be used to reset the electrical device in the event that operating power from the underwater cable 2 is lost or in the event that batteries are not present or possibly present and not active.

The electrical device 18 can also include receiver circuits for receiving outgoing data as well as driver circuits 203 for incoming data connected to coding/decoding circuits 202. The circuits 201 for receiving outgoing data can include a voltage divider 62 and a comparator 63 which can be arranged for to reformulate the outgoing data signals before they are decoded by the encoding/decoding circuits 202.

The input data driver circuits 203 may be configured in various ways to include any suitable driver circuit capable of driving an input data signal through any number of suitable connection arrangements between the electrical device 18 and the underwater cable 2.1 the preferred embodiments, the driver circuit 203 is designed to drive a coupling transformer for incoming data and which inductively connects the wet unit 30 to the underwater cable 2.

The coupling transformer for incoming data can comprise a secondary side which comprises the coil which is arranged in the outer sheath 15 of the underwater cable 2 as well as a primary side which comprises the coil which is arranged in the electrical device 18.1 certain designs, the coupling transformer for the incoming data can have a leakage inductance of about 70% or more, e.g. 94% or more (ie a coupling coefficient of about 0.3 or less, eg about 0.06 or less). Under these conditions, the driver 203 which drives the primary side of the input switching transformer will actually drive an inductive load where about 94% or more of the load is leakage inductance. The input driver circuits 203 preferably drive the primary side of the input switching transformer with a signal which enables the desired data signal (eg a Manchester signal) to be reproduced on the secondary side of the transformer.

The working function of the driver circuit 203 for incoming data will appear from fig. 43.1 operation both transistors 216 and 218 are normally in the ON state with negative output current lut. A transition from negative to positive for the input signal on the incoming data lines in the underwater cable 2 is triggered by briefly switching OFF the transistor 216 and switching ON the transistor 220. The transistor 216 can be switched OFF for a time period equal to half the resonance period of the capacitor 222 and the inductance 231 (around Va of a bit time). As the current in the inductance cannot be changed instantaneously, current will flow into the capacitor 222 during the next % of the resonance period. The current will then reverse direction and flow from the capacitor 222 to the inductance 231 in the opposite direction. This produces a transition from negative to positive value of the incoming signal on the distribution line for incoming data. Transistor 220 is then in the OFF state, while transistors 217 and 219 are both in the ON state with the current being positive.

In a similar way, a transition from positive to negative state for the incoming signal on the distribution lines for incoming data in the underwater cable 2 is triggered by the transistor 217 being briefly switched off while the transistor 220 is switched ON. Transistor 219 may be turned OFF for a time period equal to half the resonant period of capacitor 222 and inductance 231 (eg, one quarter of a bit period). Since the current in the inductance cannot be changed instantaneously, current will flow into the capacitor 222 during the next quarter of the resonance period. The current will then reverse and flow from the capacitor 222 to the inductance 231 in the opposite direction. This produces a transition from negative to positive state for the incoming signal on the distribution lines for incoming data.

The resonant period of the driver circuit 203 is determined by the resonant circuit formed by the inductance 231 and the capacitor 222. The shown driver circuit is particularly advantageous because the energy stored in the capacitor 222 while the current changes direction is such that the energy loss is reduced to a minimum. Energy is alternately transferred back and forth between the inductance and the capacitor to retain the energy.

In some embodiments, the input coupling transformer has a relatively low coupling coefficient and has a secondary side which is coupled to a relatively low load impedance. It may therefore be required that the driver circuit 203 for incoming data produces a relatively high current on the primary side of the transformer 230 (eg 3.6 amperes or more). In the shown embodiment of the driver circuit 203, in fact, almost all of the current flowing in the circuit (3.6 amps) can be caused to change direction with only a minimum of energy loss. This is a remarkable result, as the input driver circuit 203 can only draw from V9 a small fraction of the current flowing in the transformer 230. In the circuit shown in fig. 43, the input driver circuit 203 requires only a fraction of an ampere input (eg, 0.24 amps from a 10V source). In certain embodiments, a current of 3.6 amps flowing in the primary side of the input data switching transformer can actually produce a peak-to-peak signal of 1.1V on the input data line even when the transformer's leakage inductance is large. A power source, such as power source 239 in switch mode, supplies operating current Ide (eg, 3.6 amperes or more) from source V9 with an efficiency of about 85% or more.

The work function for the control logic 224-228 will appear from fig. 36A, 36B. Manchester data (DATOUT) from the encoding/decoding circuits 202 constitutes the input signal to an inverted input of the AND gate 224, to an input of the AND gate 225 to an inverted buffer 226 and to a buffer 227. A commutation drive signal CDRV constitutes input signal to the inverted input for the AND gates 224 and 225 and to the buffer 228.

The signal output from the AND gates 224 and 225 and the buffers 226-228 drive the gates for the MOS power transistors 216-220. As shown in fig. 43, the DRV+ signal is pulsed to a positive value during % of a bit time (Tb) at any time it is desired that the input data signal appearing on the input data distribution lines in the submarine cable should be subject to a transition from negative to positive. In a similar way, the DRV signal is pulsed positive for Vi of a bit time (Tb) at any time it is desired that the input data signal acting on the input data distribution lines in the underwater cable 2 should perform a transition from positive to negative.

The shown MOS power transistors 216-220 as well as the driver circuit control logic 224-228 are examples of an embodiment of the invention and may be replaced with any suitable alternative arrangement. A bipolar transistor with a diode connected between emitter and collector can e.g. replace the MOS power transistors 216-220. In certain embodiments, the input to the gate drivers 224-228 can be regulated directly by a microprocessor 204 or other suitable regulation

logic to produce the DRV+ and DRV- signals shown in fig. 43.

The driver circuit 203 has as a working function to connect incoming data from the electrical devices 18 to the underwater cable 2 after encoding from the encoding/decoding circuits 202. The driver circuits 203 for incoming data can be configured to drive the input data signals with sufficient power to bring the couplers 16, 32 to substantially degree to drown out any signal that is applied to the distribution lines for incoming data from the driver circuits 150 located in the amplifiers 25 (see Fig. 40). In some of the preferred embodiments, the input data channel for the amplifiers is continuously active at e.g. to send idle signals. These idle signals may originate as noise amplified by the rear amplifier. When an electrical device 18 is commanded by the control processor 21 (FIGS. 3-6) to respond, the electrical device 18 may be configured to simply "blow out" a response into the distribution lines for the incoming data by drowning out any present signal that is sent from an amplifier circuit 25. The regulation processor 21 preferably time multiplexes requests to the electrical devices 18, so that these electrical devices 18 do not come into conflict with each other in an unfortunate way.

During periods when no response signals are sent out from the electrical devices 18, the synchronization of the phase-locked loops 165 (see Fig. 41) in the decoding circuits 173 for the amplifiers 25 can be maintained by means of idle signals. Since the electrical devices 18 are synchronized with the amplifiers, however, as discussed above, the devices 18 can simply output a response signal into the incoming data distribution line with sufficient power to mask any data/idle signal transmitted by the amplifier driver circuit 150 which is connected to the aft end of the distribution line for incoming data. In this way, a block warning signal will not be required in addition to the reply sent out on the distribution line for incoming data by the electrical devices 18 to synchronize the phase-locked loops in the amplifiers. The waiting time will thereby be reduced to a significant extent.

The encoding/decoding circuits 202 perform a similar function to the encoding/decoding and/or connection control circuit 154 described above. The encoding/decoding circuits 202 may be connected to the microprocessor circuits 204 directly or through one or more data link control circuits 206. If the data link control circuit 206 is used, in some of the preferred embodiments the data link control circuit 206 is preferably a high-level integrated data link control circuit (HDLC ) with part number MT8952, manufactured by Mitel. In these embodiments, the data connection regulation can be carried out by the regulation processor 21 as well as by each of the electrical devices 18.

The microprocessor circuits 204 are preferably connected to one or more circuits such as the data store 220 and/or one or more regulated circuits 205. The microprocessor circuits 204 may comprise one or more microprocessors or other logic circuits, such as a Motorola 68HC11 and/or Motorola 56002. Depending the particular application, type and location of the electrical devices 18, the microprocessor circuits 204 can be configured to control one or more of the functions in the regulated circuits 205.

The regulated circuits 205 can be configured in different ways to be able to perform one or more work functions. The control circuits 205 can e.g. include one or more of the following functions: a) compass/heading, b) yaw/roll, c) acceleration, angular positions, magnetic fields, optical determination of distance/direction, buoyancy, position detection sensors, such as Hall effect sensors for to monitor e.g. the position setting of the wing plates, d) motors, e) depth sensors, and f) acoustic distance meters. In some of the preferred embodiments, the compass function forms a first electrical device, while the level-determining functions (motors, depth sensors, position detectors, bump/roll detection) form a second electrical device, and the acoustic distance measuring functions form a third electrical device. In some of the preferred embodiments, only the electrical device that performs the level-determining function is equipped with batteries 212.

Fig. 45 shows a detailed block diagram of the encoding/decoding and/or clock recovery circuits 202 for one of the preferred embodiments of the electrical devices according to the invention. The decoding circuits for output data in fig. 45 is of a similar nature to the decoding circuits for outgoing data in fig. 41 and is denoted by a corresponding reference number. The operating function for the circuits 155A-161A and 164A is e.g. substantially the same as the operating function of circuits 155-161 and 164 discussed above with reference to FIG. 41. Operating details for these circuits will not be repeated with regard to the working function of the electrical circuits 18.

In the circuit shown in fig. 45, the bit rate clock from the second DPLL 164A, the non-return-to-zero (NRZ) output data from the sampler 161A, and the BPSK clock from the first DPLL 156A form the output signal to the data link control circuit 203.

The part of fig. 45 relating to incoming data shows a modulator 168 for modulating the incoming NRC data from the data connection control circuit 203, as well as a sampling circuit 169 for performing random samples on the incoming data. A divide-by-N divider circuit, such as a counter, divides the BPSK CLK signal down to the carrier frequency of the incoming data, which in the preferred embodiment is 32 kHz. The split BPSK CLK signal constitutes the input signal to the sampling circuit 169. This sampling circuit 169 utilizes the split BPSK CLK signal to perform sampling of the incoming data. In this way, the incoming data can be synchronized with the outgoing data in each of the electrical devices 18.

The sampling circuit 169 outputs an input Manchester data signal to the input drivers 203 (shown in Figs. 42A, 42B) as well as to an edge detector 170. The edge detector 170 outputs a commutation drive signal (CDRV) to the input driver 203.

Part V: Communication with underwater cable in case of power failure

There are subsea cable operating conditions where it may be advantageous to communicate with units in the hydrophone cable and wet units when the subsea cable's main power is turned off. In order to work without power supplied from the cable, the units in the hydrophone cable and the wet units preferably include backup batteries. Due to battery power being limited, a low power communication mode is preferred. One aspect of such a low-power communication mode preferably includes bypassing the amplifiers along the outgoing data lines, the incoming data lines, or both.

In fig. 40, it is shown that an embodiment of backup communication mode includes bypass switches 53 for bypassing an amplifier along the incoming data lines. The switches 53 are preferably magnetic locking relays, as these maintain power and have very low contact resistance. Control circuit 52 sets the switches to the bypass condition when the main power to the hydrophone cable is turned off. In the position indicated in fig. 40, the switches 53 are in primary communication mode. The switches 53 provide redundancy contacts, as shown, to further increase reliability.

When the control circuit 52 moves the switches 53 to the bypass position, the incoming data line becomes an uninterrupted line through the cable, as the amplifiers are bypassed. The incoming data windings for the couplers are then connected across the incoming data line.

A commonly known communication system can be used for communication along the line for incoming data and which runs along the entire length of the cable in a back-up mode. US Patent No. 4,912,684 states, for example, a common communication system which can function as a backup communication system in the present invention.

Another aspect of a back-up communication mode concerns circuits inside the individual devices for communication over the uninterrupted line. In the embodiment shown, the incoming data line preferably works in half-duplex mode when the cable's main power is switched off. As a consequence of this, the coils for incoming data in the wet units and in the hydrophone cable devices preferably comprise circuits capable of receiving data from the search vessel. Figs. 42A and 42B show backup communication circuits 202', primary communication circuits 202, and switches S1 and S2, which can switch between primary and backup communication modes in an electrical device. Microprocessor 204 preferably controls switches S1 and S2. When the main cable power is turned off, Vpwr will approach zero and the microprocessor 204 will activate the switches S1, S2 to switch to the backup communication circuit 202'. The backup communication circuits 202' preferably comprise coding and decoding circuits which are configured to encode incoming data and decode outgoing data using conventional modulation techniques, e.g. frequency modulation (FM) or phase modulation (PM). In backup mode, the devices can communicate with a lower bit rate (e.g. 4 kbps) than in the primary communication mode. In this way, the electrical devices are able to communicate with the search vessel even when the main cable power is switched off and battery energy is conserved.

Part VI: Fault-tolerant designs

A common failure case for the underwater cable's power distribution and/or data communication equipment 20 is the loss of one or more electrical devices along the underwater cable 2. Effective power distribution to the electrical devices 18 from the underwater cable 2 preferably takes place by using coordinated power transmission circuits. However, it has been found that in the event of the loss of one or more electrical devices 18 along the underwater cable 2, the bandwidth for the tuned power transmission circuits will often decrease, which makes outgoing data communication difficult in designs with combined data/power transmission.

In accordance with the present invention, the reliability problems in connection with such a failure case can be reduced by dividing the data/power distribution lines as discussed above and/or by including a load adjusting circuit 188 (see Fig. 46) in the underwater cable's power distribution and/or data communication equipment 20. The load adjusting circuit 188 may be arranged at any location along one or more data/power lines, such as e.g. in one or more of the electrical devices 18 in the hydrophone cable, in the amplifier drive circuits or in the amplifier-receiver circuits, in the couplers and/or in the terminations

34, 44.

Another common fault in the submarine cable's power distribution and/or communication equipment is the intrusion of seawater, which creates a short-circuit load on the power distribution and/or data communication lines. This short-circuit load can reduce the bandwidth of the tuned circuits in the driver 50, making outgoing data communication difficult in designs for combined data/power transfer.

In accordance with the present invention, the reliability problems that arise in such a case of failure can be reduced by including a load adjustment circuit 188' (see Fig. 46) in the submarine cable's power distribution and/or data communication equipment. This load adjusting circuit 188' is preferably arranged in the driver circuit, as shown in fig. 9 and 40.

In one of the preferred embodiments, the load compensation circuit 188, 188' comprises two oppositely coupled zener diodes coupled across the power distribution line at or near the receiver 152. Other locations are also suitable. By reverse connection it is meant that the zener diodes are connected in series across the data/power distribution lines with cathode to cathode or also in an anode to anode configuration. In fig. 40 is e.g. the load adjusting circuit 188, 188' shown as two cathode-coupled zener diodes which are connected across the distribution lines for output data and/or power.

Other configurations of the load adjusting circuit are also possible. The circuit can e.g. include one or more voltage sensors which monitor the voltage on the power distribution line and which switch in different resistance values in response to a change in the voltage level. The load adjusting circuits work to regulate the changes in bandwidth for the power transmission circuits, e.g. due to the loss of one or more inductively coupled loads along the submarine cable. This design is also easier to put into operation as it does not require any load from a wet unit 30 on unused locations.

In preferred embodiments, it may be desirable to dimension the load adjustment circuit (e.g. zener diodes) so that a voltage rise as a result of a skewed setting of the coils in the coupler within the tolerance limit (e.g. length/width of the pole surface) does not trigger it load adjusting circuit for active operation. Activation of certain designs of the load adjustment circuit can produce reduced power transfer efficiency along the data/power distribution lines. The load adjustment circuit 188, 188' can therefore be designed to operate just above the voltage rise value attributable to the fact that one or more copies are misaligned within the coupler tolerance.

When a fault along the data/power distribution line occurs, load can be removed. When load is removed, the voltage along the power distribution line will usually rise due to the Q value of the distributed filter increasing. The load adjustment circuit is preferably configured to add loss to the circuit to keep the Q value of the circuit relatively constant, so that the bandwidth of the distributed filter does not change.

In preferred embodiments, the load adjustment circuit 188, 188' may allow the Q value to increase about 10% or more before the load adjustment takes place and reduces the peaks of the waveform. This is particularly important in the event that power and data are distributed on the same line. When data and power are distributed on the same line, it may be desirable to maintain the load resistance close to the intended nominal value so that the distributed filter can work with the correct data bandwidth. If the voltage on the power distribution line increases above a set nominal value, the filter bandwidth may decrease and the data waveform may be distorted. It can then be difficult to demodulate data in the next amplifier, and the data communication channel can then be interrupted.

A load regulating circuit 188, 188' comprising zener diodes can be particularly advantageous, as the diodes do not conduct and therefore do not consume precious power resources when all electrical devices are in operation. The Zener diodes are also simple, easy to put into operation and add no significant additional weight to the underwater cable 2.

Part VII: Hierarchical load shedding

The main power line 23 in the underwater cable 2 supplies power to several separate electrical devices 18. Each of these electrical devices 18 can be designed to draw a predetermined current, as determined from a total power budget for the underwater cable 2. When a fault occurs along a of the several data/power distribution lines or in the electrical devices 18 connected to the line, the current drawn from the data/power distribution lines may, however, exceed the maximum allocated, predetermined load. In extreme cases, the voltage on the main power line can be degraded, and the entire underwater cable will then be out of service. In less extreme cases, and particularly in the case that power and data are connected to a single data/power distribution line, data transmission through said multiple amplifiers can become ineffective over the data section with errors.

In many embodiments, it may consequently be desirable to implement the second power circuit 52 in each of the power conversion circuits 50 (Fig. 8) as a current-limited power source. In this way, power supplied to a power distribution line in a particular cable section will never exceed the allocated maximum current. A fault along that section of cable simply causes the voltage along that section of cable to drop, while the current remains essentially constant.

This voltage drop can have an adverse effect on the electrical devices 18. Power transferred to the electrical device 18 can be reduced to the point where all electrical devices 18 cannot function. By using a hierarchical load disconnection technique, however, it may be possible to maintain certain electrical devices 18 and/or corresponding electrical functions in operation while others are disconnected or switched off. If certain electrical devices and/or electrical device functions are to be switched off, the loads assigned to these functions will preferably be switched off in the opposite order of the relevant function's critical importance for the underwater cable 2 and the power distribution and/or data communication equipment 20.

Hierarchical load shedding can be controlled by any circuit throughout the system, including the control processor 21, the amplifiers 25 and/or the electrical devices 18. Furthermore, the hierarchical load shedding within each of these circuits can be configured in different ways.

In certain embodiments, it can e.g. it may be desirable to disconnect one or more loads depending on the voltage level on one or more data/power distribution lines within the underwater cable 2.1 other designs, it may be desirable to disconnect one or more loads based on other factors, such as loss of communications to the electrical devices 18.

Each electrical device 18 can be considered a load in itself or can itself contain one or more loads. Each electrical device can e.g. include one or more work functions, as indicated by the regulating circuits in Figures 42A, 42B. A load can be understood to be any electrical load assigned to one or more, or possibly all work functions for a certain electrical device 18.

The regulation and/or error detection for initiating the load disconnection can also be arranged in one place or distributed in several places along the underwater cable.

The fault detection circuits (e.g. a voltage detector and/or an A/D converter) can e.g. be located in the individual electrical devices 18 and/or in the amplifiers, while the regulation of the load disconnection can be located in the electrical devices, in the amplifiers and/or in the regulation processor 21. Although regulation of the hierarchical load disconnection can be controlled by a single processor (f .eg the regulation processor 21) in certain of the preferred embodiments, this control of the hierarchical load disconnection is distributed among the several electrical devices 18 (eg programmed into the microprocessor 204), each of which works independently. This distributed regulation of the load shedding function has been found to provide increased reliability.

A first exemplary embodiment of a hierarchical load disconnection function put into operation in the underwater cable's power distribution and/or data communication equipment 20 is shown in flowchart form in fig. 47.1 fig. 47, function step 250 determines whether the electrical device 18 is in low power mode. If power and/or data communications to the electrical device are at normal levels, step 251 is initiated.1 function steps 251 and 252, the power level and/or data communications are continuously monitored to determine whether a fault condition exists. When a failure condition is detected, functional step 253 is performed.1 step 253 a single load (eg loads a-e) is removed by e.g. to reduce the power of the circuit that controls and/or performs the functions belonging to this load. This can be an electrical device 18 in its entirety or parts of circuits located in an electrical device 18. The particular load that is selected is preferably selected in a hierarchical order, where some of the preferred order e.g. are: a) acoustic distance measurement, b) compass, c) depth determination to set a new immersion depth, d) depth reporting to report the current immersion depth, and e) depth regulation to maintain the determined depth. In this embodiment, the least important/critical functions are then removed first.

After a load (e.g., a device or function in a device) has been removed, in embodiments where the load cutoff regulation is distributed, an electrical device will wait for other electrical devices 18 to also remove their loads (step 254). The electrical device can wait a predetermined time period and/or a varying time period based on the stability of the received voltage during a given time period. The electrical device 18 will then test whether the fault condition still exists. If the error condition is no longer present, the electrical device 18 will enter active low power mode (step 257) and return to start. If, however, the fault is still detectable (step 256), the electrical device will again go to step 253, until all loads assigned to a particular electrical device have been reduced in power.

If all loads are derated and the fault is still present (step 256), an electrical device for immersion control or so-called bird will still maintain a substantially constant immersion depth (possible using only battery power) (step 259), setting the active low power mode (step 257), and return to the initial step. Other electrical devices 18 without a depth deregulation function will preferably set active low power modes (step 257) and return directly to the starting step.

When low power mode is active, in process steps 260-261 the electrical device 18 will preferably continue to monitor the underwater cable 2 to detect whether the fault condition still exists. When a voltage level is utilized to determine a fault condition, it is desirable to set the voltage level to indicate cancellation of the fault to a higher value than the voltage level for detecting the fault. These different voltage levels will produce a hysteresis, so that the equipment will not oscillate continuously between a fault state and a fault absence state.

If the fault condition has been cleared, in step 262 loads will be applied in reverse hierarchical order (one load per repetition) until the fault condition is resolved. By reverse hierarchical order is meant that the loads are preferably reconnected in the opposite order to the order that was used when removing the loads. In many cases, this order will be such that the most important loads are restored first (eg in the load order e-a).

After adding a load, in a distributed regulation configuration the regulator will wait for the other regulators to add loads in step 263.1 step 264 a test is carried out to determine whether all loads have been applied. If all loads have been applied, the low power mode is made inactive (step 265) and control is returned to the initial step. If more loads remain inactive, function step 260 is initiated again and the process continues as discussed above.

In step 256, the error condition may simply be a determination to confirm that the communications with the control processor 21 are out of order.

In other embodiments, the fault condition can be determined if the voltage received from the underwater cable 2 is below a fixed value (preferably programmable).

In still other embodiments, the fault condition detection in step 256 may be based on multiple predetermined voltage threshold values (preferably programmable) with a different predetermined voltage level assigned to each load identified in step 253. If, for example, during the first iteration the electrical loads assigned to the acoustic distance measurement function can be removed if the received voltage from the underwater cable is below a first predetermined voltage level, e.g. 9.5 volts. In another iteration, the electrical loads assigned to the compass function may be removed if the received voltage from the underwater cable is below another predetermined voltage level, e.g. 9 volts. On a third iteration, the electrical loads associated with the depth setting and recording functions can be removed if the received voltage from the underwater cable is below a third predetermined voltage level, e.g. 8.5 volts. Process step 258 then determines whether there are any loads left to disconnect at a certain voltage level.

In alternative embodiments, the fault condition may be determined if the received voltage from the submarine cable 2 is below a predetermined value (preferably programmable), and rather than removing the loads individually, as discussed above, all loads may be removed simultaneously in step 253. If the voltage received from the underwater cable is below a predetermined voltage value (e.g. 9.5 V, 9.0 V, or 8.5 V), then in this embodiment all loads will be removed simultaneously in step 253. The electrical devices can then return to start mode and in idle wait to receive command signals from the amplifiers 25 (when a load disconnection intelligence, e.g. a CPU is placed in the amplifiers) and/or the control processor 21. These command signals can then be used to optionally connect one or more loads to a faulty cable section depending on the severity of the fault and the particular function required in the present case. In this way, the control processor and/or the amplifier can control operation in degraded mode where the individual loads are time multiplexed for adaptation to the fault condition.

In still other alternative embodiments, after all loads have been removed in the single process step 253, the program will continue to set the active low power mode and enter the low mode section of the program. In step 261, each load can then be reconnected in hierarchical order where the most critical loads are reconnected first. Certain design examples can, on a first iteration, e.g. the electrical loads assigned to depth setting, recording and regulation functions are activated if the voltage received from the underwater cable is above a first predetermined and/or programmable voltage level, e.g. 8.5 volts. In another iteration, the electrical loads assigned to the compass function can be activated if the received voltage from the underwater cable 2 is above another predetermined and/or programmable voltage level, e.g. 9 volts. At the third iteration, the electrical loads associated with the acoustic rangefinder function can be activated if

the received voltage from the underwater cable is above a third

tuned and/or programmable voltage level, e.g. 9.5 volts.

Other alternative modes of operation can also be implemented to enable hierarchical load shedding. The regulation in these functional modes can be entirely within the electrical devices, amplifiers and/or the regulation processor. Alternatively, the regulation of the hierarchical load disconnection can be distributed between one or more of the amplifiers, the electrical devices and/or the regulation processor. One of the preferred designs for hierarchical load disconnection is illustrated as an example in the state diagrams fig. 48, 49. Fig. 48 shows the hierarchical load disconnection assigned to different devices, such as an assigned depth control device or level bird, an assigned compass/course device, or an assigned acoustic device, each of which has several work functions to be disconnected hierarchically.

As indicated in fig. 48, the electrical device can go from a reset state 270 into an idle state 271. In this idle state 271, communications with the device are possible. If the voltage detected by the electrical device when using e.g. The A/D converter 214 in FIG. 42A, 42B are smaller than Vi_o, e.g. 7 volts, and the battery is dead, then the electrical device will enter shutdown state 272 and perform a clean shutdown of ongoing processes before cutting off the power supply for a dead state. If the voltage Vpwr which is supplied by the main power line and detected by the electrical device exceeds Vm, then the device from the dead state will again enter the idle state 271. VHi is preferably about 9.5 volts for an acoustic device, about 9.0 volts for a compass/ heading device, as well as 8.5 volts for a depth control device or level bird. In the idle state, communications between the electrical device and the control processor 21 are still possible.

If the device receives a command signal (CMD), the device will be able to enter a main-powered active state 273 from the idle state 271 if

Vpwr is greater than or equal to VLo- The device can enter a battery-powered active state 274 if the command signal is received and Vpwr is less than VLo- A command signal can be issued from the regulation processor 21 or from the amplifiers. If the device is in either a main-powered active state 273 or a battery-powered active state 274, and the device receives a CMD signal, the device may re-enter idle state 271.

If the electrical device in the main powered active state 273 shows that Vpwr is less than VLo, then the device can enter the battery powered active state 274. The hysteresis between VLo and Vm prevents the device from swinging between the battery powered and main powered active state.

In the battery powered active state 274, the electrical device can continuously monitor the battery voltage level. If the battery voltage drops below a predetermined level, e.g. around 7 volts, the device may enter shutdown mode 272 before entering the dead state. As indicated above, the control processor 21 or the amplifiers can instruct the device to enter the cycle state 271 by sending out a command signal (CMD).

If a device performs several functions, the device can get rid of one or more of these functions. As shown in fig. 47, the loads can e.g. is disengaged hierarchically.

The hierarchical order of load disconnection can be controlled by different voltage levels set for each electrical device to enter a

off/idle state and/or to return to an idle/active state. When the power supplied to the electrical device 18 e.g. is below 9.5 volts, can e.g. the acoustic function and/or device be the only load to enter or remain in the off state and/or the idle state (the acoustic device can, for example, be reactivated at 9.5 volts). In alternative embodiments, it can

acoustic device be the first device to enter a switched-off state or idle state at e.g. 9.5 volts. If the voltage supplied to the electrical device 18 is below e.g. 9 volts, the acoustic device and compass may be in an off or idle state. If the voltage applied

the electrical device 18 e.g. is below 8.5 volts, then similarly the leveling bird may enter battery backup mode, while the acoustic device and compass may be in an idle or inactive state.

Referring to one of the preferred embodiments shown in fig. 47-49, it will appear that when the voltage is below 7 volts, all electrical devices will enter an idle state where only communications with the drying electronics 5 are maintained with other loads in the electrical devices 18 switched off. If the voltage is still below 7 volts, all electrical devices will go into a switched off state. From the off state, in the embodiments shown, the level setting devices or level birds will return to the idle state when the voltage rises above 8.5 volts, while the compass devices will return to the idle state when the voltage rises above 9 volts, and the acoustic devices will return to the idle state when the voltage rises above 9.5 volts. In this way, the electrical devices in the embodiments shown can independently reactivate themselves in response to programmable voltage levels keyed to the critical level for each function of the electrical devices.

A distinctive feature of the designs of the electrical devices 18 shown in fig. 49 is that these electrical devices carry out the hierarchical load disconnection completely independently. Each of the load shedding programs and state diagrams shown in Figs. 47-49 can e.g. is performed by the microprocessor 204 without communication with other wet units and/or the regulation processor 21.

The term hierarchical load shedding is intended to broadly cover configurations where the load on the power line in the submarine cable is reduced in a specified order in response to one or more fault conditions, as discussed here.

Regulation of the different communication modes can take place in the individual electrical devices. If in fig. 49 e.g. is a power failure in the underwater cable or interrupted external power supply to the devices, Vpwr in fig. 42A and 42B go to zero. The devices enter state 180 and initiate backup communication mode as discussed above. When the power supply is restored, the devices can enter primary communication mode, as indicated by condition 281.

In alternative embodiments, the amplifiers may include a CPU, voltage sensors and other control circuitry designed to enable the control processor 21 and/or the amplifier to connect additional power to the affected data/power distribution lines in the event of a failure. Each amplifier can e.g. comprise a redundant driver circuit which can possibly be switched into operation by the regulation processor 21 and/or by the individual amplifiers in response to a fault on a specific distribution line. Instead of selectively reducing the load along a certain cable section, in this way the power input can be selectively increased to compensate for the error.

A notable result of a combination of various aspects in embodiments of the present invention is that power can be reliably transferred to the wet units 30 with an overall power transfer efficiency of about 60% or more. This remarkable result makes it possible to supply power to the wet units exclusively from the underwater cable, and has eliminated the necessity of supplying operating power when using batteries in practical applications of underwater hydrophone cables. Furthermore, significant improvements have been made with regard to the reliability of the underwater cable's power distribution and communication equipment 20.1 In addition, the waiting time for data transmission from the electrical devices 18 is reduced to a minimum even when amplifiers are used.

Although the present invention has been shown in connection with a towed seismic hydrophone cable, it will be understood that it will also be able to be used in other instrumented underwater cables, such as any towed hydrophone cable, whether it is used for geophysical, scientific or military purposes, or for non-towed cables with bottom reference. In any of these applications, the submarine cable may be oriented horizontally, vertically, or at any angle to the horizontal and vertical.

Although several examples of implementations of power distribution and communication systems have been shown, as well as elements for building up the objects of the present invention have been shown, it will be understood that the inventions are not limited to these implementations. Modifications can be made by professionals in the field, particularly in light of what appears from the preceding description. In certain embodiments, it may thus be desirable to distribute power to the electrical devices 18 on both the incoming and outgoing data distribution lines. In this way, the total power distributed on each line can be reduced. Furthermore, elements from the different designs can be combined with and/or used instead of corresponding elements in another design. In addition, alternative embodiments of the invention may include more or fewer components than is the case in the embodiments shown. Each of the shown designs can e.g. utilize one or more of the special features, circuits and/or functions specified in other embodiments. It is therefore intended that the subsequent patent claims shall cover all such modifications in any combination which include distinctive features of the invention or are contained within the idea of the invention

scope and conceptual framework.

It should therefore be understood that the invention encompasses all possible combinations and sub-combinations of the elements described here. Each of the embodiments shown or described can e.g. utilize one or more of the features, components and/or functions used in other designs. Furthermore, the description is divided into parts I-N/II to facilitate the understanding of the invention. However, many aspects of the invention span more than one of these parts of the description. For example the amplifiers in an underwater cable can include elements that distribute power, synchronize data and react to errors. As a consequence of this, the amplifiers act in part I: power distribution/communication equipment, part IV: synchronization of input/output data, and part VI: fault-tolerant structures. Other aspects of the invention span one or more of the parts of the description. The different aspects of the invention may be related to each other and are not limited to one or more of the parts of the description.

Claims (20)

1. Procedure for distributing power under water, comprising that the power is transmitted at a first frequency on a main power line (23) in an underwater cable (2); characterized in that the method further comprises. that the power on the main power line (23) is converted to a second frequency, higher than the first frequency; and that the power at the second frequency is distributed through several power distribution lines (28A-28C, 38A-38C, 41, 42, 46, 47) to several devices (18, 30,31), which are placed selectively along the underwater cable (2). 2. Method according to claim 1, characterized in that the first frequency is direct current with a frequency equal to zero. 3. Method according to claim 1, characterized in that the first frequency is in the range 1kHz to 4kHz. 4. Method according to claim 1, 2 or 3 characterized in that the second frequency is in the range 25kHz to 400kHz. 5. Method according to one of the preceding claims, characterized in that the transformation of the power on the main power line (23) comprises that the power signal is transformed into a direct current signal, and then the direct current signal is transformed into the power distribution signal at the higher frequency. 6. Method according to one of the preceding claims, characterized in that the power distribution signal at the higher frequency is inductively coupled from the power distribution line (28A-28C, 38A-38C, 41, 42, 46, 47) through a screen (15) on the cable (2) to the device (18,30). 7. Method according to one of the preceding claims, characterized in that data is transmitted on the power distribution lines (28A-28C, 38A-38C, 41, 42, 46, 47). 8. Method according to claim 7, characterized in that the data transmission on the power distribution lines (28A-28C, 38A-38C, 41, 42, 46, 47) includes data being coded on the power distribution signal. 9. Method according to claim 8, characterized in that the coding of data on the power distribution signal includes outgoing data being coded on the power distribution signal. 10. Underwater power distribution system for supplying several devices with power, comprising an underwater cable (2), where the devices (18,30,31) are laid out along the underwater cable (2); characterized in that the system further comprises: a main power line (23) which extends through the underwater cable (2) and is arranged to transmit a main power signal at a first frequency; and several conversion circuits (50) arranged distributed along the underwater cable and connected respectively between the main power line (23) and the several devices (18,30,31), each conversion circuit (50) being arranged to convert the main power signal into a power distribution signal at a second frequency which is higher than the first frequency. 11. System according to claim 10, characterized in that each conversion circuit (50) is arranged to convert the main power signal to a direct current signal and then to convert the direct current signal to the power distribution signal. 12. System according to claim 10 or 11, characterized in that each conversion circuit (50) is arranged to convert a direct current main power signal into an alternating current power distribution signal with a frequency in the range 25kHz to 400kHz. 13. System according to claim 10 or 11, characterized in that each conversion circuit (50) is arranged to convert an alternating current main power signal with a frequency in the range 1kHz to 4kHz into an alternating current power distribution signal with a frequency in the range from 25kHz to 400kHz. 14. System according to one of claims 10 to 13, characterized in that it comprises several power distribution lines (28A-28C, 38A-38C, 41, 42, 46, 47) where each power distribution line (28A-28C, 38A-38C, 41, 42, 46, 47) is connected to a power conversion circuit ( 50) and is designed to transmit the power distribution signal. 15. System according to claim 14, characterized in that the first and second power distribution lines (41, 42, 46, 47) extends in the opposite direction from a power conversion circuit (50) along the cable (2). 16. System according to claim 14 or 15, characterized in that the underwater cable (2) includes an outer shield (15) to which devices (18, 30) are attached and that the power distribution system further comprises one or more couplers (16, 16', 16"), which are electrically connected to a power distribution line ( 28A-28C, 38A-38C, 41, 42, 46, 47) to inductively couple the power distribution signal through the screen (15) to the device (18,30). 17. System according to claim 14, 15 or 16, characterized in that it includes an encoding circuit (154,171) connected to a power conversion circuit (50) to encode data onto the power distribution signal. 18. System according to claim 17, characterized in that the coding circuit (154,171) is arranged to code outgoing data on the power distribution signal. 19. System according to claim 17 or 18, characterized in that it comprises a driver (150, 151), connected to the power distribution line (28A-28C, 38A-38C, 41,42,46, 47), to drive a power distribution signal carrying data and power along the power distribution line (28A-28C , 38A-38C, 41, 42, 46, 47). 20. System according to one of claims 10 to 19, characterized in that it comprises a data channel (48) which extends along the cable (2) and several hydrophones (7) placed along the cable (2), where the hydrophones (7) transmit hydrophone information over the data channel (48).